sql: make valueToText() operate on MAP/ARRAY values

Since ARRAY and MAP cannot be converted to SCALAR type, this
operation should throw an error. But when the error is raised in
SQL, it is displayed in unreadable form. The reason for this is
that the given array or map is not correctly converted to a
string. This patch fixes the problem by converting ARRAY or MAP to
their string representation.
For example:

box.execute('CREATE TABLE t1(i INT PRIMARY KEY, a SCALAR);')
format = {}
format[1] = {type = 'integer', name = 'I'}
format[2] = {type = 'array', name = 'A'}
s = box.schema.space.create('T2', {format=format})
i = s:create_index('ii')
s:insert({1, {1,2,3}})
box.execute('INSERT INTO t1 SELECT * FROM t2;')

Should return:
- error: 'Type mismatch: can not convert [1, 2, 3] to scalar'

Follow-up #4189

(cherry picked from commit 736cdd81)