[3.11] gh-106052: Fix bug in the matching of possessive quantifiers (GH-106515) (GH-107795)

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)