[3.14] gh-138860: Lazy import rlcompleter in pdb to avoid deadlock in subprocess...

[3.14] gh-138860: Lazy import rlcompleter in pdb to avoid deadlock in subprocess (GH-139185) (GH-139305) (GH-139280)

* gh-138860: Lazy import rlcompleter in pdb to avoid deadlock in subprocess (GH-139185)
(cherry picked from commit c8624cd36746b17d8f991cde63705e9419e940de)

* gh-139289: Lazy import rlcompleter to fix the refleak (GH-139305)
(cherry picked from commit 8288f3693f50058ad9b9fe04e01f5dad902d8bad)

Co-authored-by: Tian Gao <gaogaotiantian@hotmail.com>