box: reduce luaT_pushtuple Lua GC memory usage

<luaT_pushtuple> function created a new GCfunc object for a tuple __gc
handler (i.e. <lbox_tuple_gc>), having no upvalues, on each call when
tuple object for Lua world is created.

The change introduces the reference to the single GCfunc object created
on Tarantool startup and stored to Lua registry. Using this approach in
scope of <luaT_pushtuple> is aimed to reduce Lua GC memory usage.

Part of #5201

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

Reviewed-by: Vladimir Davydov <vdavydov@tarantool.org>
Reviewed-by: Sergey Kaplun <skaplun@tarantool.org>
Signed-off-by: Igor Munkin <imun@tarantool.org>
(cherry picked from commit 8d7d1460)