[3.12] gh-106052: Fix bug in the matching of possessive quantifiers (GH-106515) (#107796)

[3.12] gh-106052: Fix bug in the matching of possessive quantifiers (gh-106515)

It did not work in the case of a subpattern containing backtracking.

Temporary implement possessive quantifiers as equivalent greedy qualifiers
in atomic groups..
(cherry picked from commit 7b6e34e5baeb4162815ffa4d943b09a58e3f6580)