test: refactor dbgr test with `it` helper

`console_debugger_session_test.lua` can be simplified and made more
stable with interactive_tarantool helper. With the new
`read_untill_prompt()` helper function, dbgr prompt can be used as
end-of-output marker instead of '...' in yaml-outputting main console.
This way, popen results are unambiguous and no retries are required.
At the same time, dbgr prompt is now expected with every result, thus
there is no need for an extra check. But `continue` command usually
reaches the end of the script and exits debugger, thus
'<END_OF_EXECUTION>' marker was introduced.
Empty stderr and header check were moved to interactive_tarantool helper.
This patch breaks the test without debugger readline support patch,
that is next in the patchset.

Part of #7738

NO_CHANGELOG=test refactoring
NO_DOC=test refactoring

(cherry picked from commit 72008443)

test/app-luatest/console_debugger_session_test.lua

 local t = require('luatest')
-local popen = require('popen')
-local tnt = require('tarantool')
 local fio = require('fio')
+local it = require('test.interactive_tarantool')
 
 local function unescape(s)
     return s and s:gsub('[\27\155][][()#;?%d]*[A-PRZcf-ntqry=><~]', '') or ''
@@ -11,17 +10,7 @@ local function trim(s)
     return s and s:gsub('%s+$', '') or ''
 end
 
-local function tarantool_path(arg)
-    local index = -2
-    -- arg[-1] is guaranteed to be non-null
-    while arg[index] do index = index - 1 end
-    return arg[index + 1]
-end
-
-local TARANTOOL_PATH = tarantool_path(arg)
-
 local DEBUGGER = 'luadebug'
-local dbg_header = tnt.package .. " debugger " .. tnt.version
 local dbg_prompt = DEBUGGER .. '>'
 local dbg_failed_bp = 'command expects argument in format filename:NN or ' ..
                       'filename+NN, where NN should be a positive number.'
@@ -146,17 +135,17 @@ local sequences = {
     12 | os.exit(0)
 ]],
         { ['\t'] = '' }, -- \t is a special value for start
-        { ['n'] = dbg_prompt },
-        { ['s'] = dbg_prompt },
-        { ['n'] = dbg_prompt },
-        { ['n'] = dbg_prompt },
+        { ['n'] = '' },
+        { ['s'] = '' },
+        { ['n'] = '' },
+        { ['n'] = '' },
         { ['p'] = 'expects argument, but none received' },
         { ['p obj'] = 'obj => {"tzoffset" = "+0300", "hour" = 3}' },
-        { ['n'] = dbg_prompt },
+        { ['n'] = '' },
         { ['p ymd'] = 'ymd => false' },
         { ['w'] = 'local hms = false' },
         { ['bogus;'] = 'is not recognized.' },
-        { ['h'] = dbg_prompt },
+        { ['h'] = '' },
         { ['t'] = '=> builtin/datetime.lua' },
         { ['u'] = '{file}:3 in chunk at' },
         -- FIXME (gh-8190) - we should not show calling side at luadebug.lua
@@ -165,15 +154,15 @@ local sequences = {
         { ['d'] = '{file}:3 in chunk at' },
         { ['d'] = 'Inspecting frame: builtin/datetime.lua' },
         { ['l'] = 'obj => {"tzoffset" = "+0300", "hour" = 3}' },
-        { ['f'] = dbg_prompt },
-        { ['n'] = dbg_prompt },
+        { ['f'] = '' },
+        { ['n'] = '' },
         { ['p T'] = 'T => 1970-01-01T03:00:00+0300' },
-        { ['n'] = dbg_prompt },
-        { [''] = dbg_prompt },
-        { [''] = dbg_prompt },
-        { [''] = dbg_prompt },
+        { ['n'] = '' },
+        { [''] = '' },
+        { [''] = '' },
+        { [''] = '' },
         { ['p S'] = 'S => "1970-01-01T0300+0300"' },
-        { ['c'] = '' },
+        { ['c'] = '<END_OF_EXECUTION>' },
     },
 
     -- partial sequence with successful breakpoints added
@@ -193,12 +182,12 @@ local sequences = {
     12 | os.exit(0)
 ]],
         { ['\t'] = '' }, -- \t is a special value for start
-        { ['b +9'] = dbg_prompt },
+        { ['b +9'] = '' },
         { ['c'] = '{file}:9' },
-        { ['n'] = dbg_prompt },
+        { ['n'] = '' },
         { ['p S'] = 'S => "1970-01-01T0300+0300"' },
         { ['p T'] = 'T => 1970-01-01T03:00:00+0300' },
-        { ['c'] = '' },
+        { ['c'] = '<END_OF_EXECUTION>' },
     },
 
     -- partial sequence with failed breakpoint addsitions
@@ -267,21 +256,23 @@ local sequences = {
     },
 }
 
-local function run_debug_session(cmdline, sequence, tmpfile, header)
+local function run_debug_session(sequence, tmpfile, flags)
     local short_src = fio.basename(tmpfile)
     --[[
         repeat multiple times to check all command aliases
     ]]
     for i = 1, MAX_ALIASES_COUNT do
-        local fh = popen.new(cmdline, {
-            stdout = popen.opts.PIPE,
-            stderr = popen.opts.PIPE,
-            stdin = popen.opts.PIPE,
-        })
-        t.assert_is_not(fh, nil)
-        -- for -d option we expect debugger banner in the stderr,
-        -- but for self invoke debugger there is no extra header.
-        local first = header ~= nil
+        local args
+        if flags then
+            args = {flags, tmpfile}
+        else
+            args = {tmpfile}
+        end
+        local expect_header = type(flags) == 'string' and flags:find("-d")
+        local child = it.new_debugger({args = args,
+                                       expect_header = expect_header})
+
+        debuglog(child:read_until_prompt(dbg_prompt))
         for _, row in pairs(sequence) do
             local cmd, expected = next(row)
             -- interpret template strings {file}
@@ -290,36 +281,22 @@ local function run_debug_session(cmdline, sequence, tmpfile, header)
                 if cmd ~= '' then
                     local key, arg = get_key_arg_pair(cmd)
                     arg = arg and (' ' .. arg) or ''
-                    cmd = get_cmd_alias(key, i) .. arg .. '\n'
-                else -- '' empty command - repeat prior one
-                    cmd = cmd .. '\n'
+                    cmd = get_cmd_alias(key, i) .. arg
                 end
-                fh:write(cmd)
-                debuglog('Execute command: "'..trim(cmd)..'"')
+                debuglog('Execute command: "' .. trim(cmd) .. '"')
+                child:execute_command(cmd)
             end
 
-            local result
-            local clean_cmd = trim(cmd)
-            -- there should be empty stderr - check it before stdout
-            local errout = fh:read({ timeout = 0.05, stderr = true})
-            debuglog('stderr output: ', trim(errout))
-            if first and errout then
-                -- we do not expect anything on stderr
-                -- with exception of initial debugger header
-                t.assert_str_contains(trim(errout), header, false)
-                first = false
+            if expected == '<END_OF_EXECUTION>' then
+                t.assert_error_msg_contains('Unexpected EOF',
+                    child.read_until_prompt, child)
             else
-                t.assert(errout == nil or trim(errout) == '')
-            end
-            repeat
-                result = trim(unescape(fh:read({ timeout = 0.5 })))
-                debuglog('stdout output:', result)
-            until result ~= '' or result ~= clean_cmd
-            if expected ~= '' then
-                t.assert_str_contains(result, expected, false)
+                local res = trim(unescape(child:read_until_prompt(dbg_prompt)))
+                debuglog(res)
+                t.assert_str_contains(res, expected)
             end
         end
-        fh:close()
+        child:close()
     end
     debuglog('Delete temporary file ', tmpfile)
     os.remove(tmpfile)
@@ -334,8 +311,7 @@ g.test_debugger = function(cg)
     local tmpfile = table.remove(sequence, 1)
     t.assert(type(tmpfile) == 'string')
 
-    local cmd = { TARANTOOL_PATH, '-d', tmpfile }
-    run_debug_session(cmd, sequences[scenario_name], tmpfile, dbg_header)
+    run_debug_session(sequences[scenario_name], tmpfile, '-d')
 end
 
 local g_self = t.group('self-debug')
@@ -352,10 +328,10 @@ local shorter_sequence = {
     8 | os.exit(0)
 ]],
     { ['\t'] = '' }, -- \t is a special value for start
-    { ['n'] = dbg_prompt },
-    { ['s'] = dbg_prompt },
-    { ['n'] = dbg_prompt },
-    { ['n'] = dbg_prompt },
+    { ['n'] = '' },
+    { ['s'] = '' },
+    { ['n'] = '' },
+    { ['n'] = '' },
     { ['p'] = 'expects argument, but none received' },
     { ['p obj'] = 'obj => {"tzoffset" = "+0300", "hour" = 3}' },
     { ['u'] = '{file}:5 in chunk at' },
@@ -363,7 +339,7 @@ local shorter_sequence = {
     { ['d'] = 'Inspecting frame: builtin/datetime.lua' },
     { ['l'] = 'obj => {"tzoffset" = "+0300", "hour" = 3}' },
     { ['f'] = '{file}:6 in chunk at' },
-    { ['c'] = '' },
+    { ['c'] = '<END_OF_EXECUTION>' },
 }
 
 -- `tarantool debug-self-target.lua`, where
@@ -372,6 +348,5 @@ g_self.test_debug_self_invoke = function()
     local tmpfile = table.remove(shorter_sequence, 1)
     t.assert(type(tmpfile) == 'string')
 
-    local cmd = { TARANTOOL_PATH, tmpfile }
-    run_debug_session(cmd, shorter_sequence, tmpfile)
+    run_debug_session(shorter_sequence, tmpfile)
 end