GH-130614: pathlib ABCs: support alternate separator in `full_match()` (#130991)

In `pathlib.types._JoinablePath.full_match()`, treat alternate path
separators in the path and pattern as if they were primary separators. e.g.
if the parser is `ntpath`, then `P(r'foo/bar\baz').full_match(r'*\*/*')` is
true.