GH-106747: Make pathlib ABC globbing more consistent with glob.glob() (#115056)

When expanding `**` wildcards, ensure we add a trailing slash to the
topmost directory path. This matches `glob.glob()` behaviour:

    >>> glob.glob('dirA/**', recursive=True)
    ['dirA/', 'dirA/dirB', 'dirA/dirB/dirC']

This does not affect `pathlib.Path.glob()`, because trailing slashes aren't
supported in pathlib proper.

Lib/pathlib/_abc.py

@@ -95,7 +95,7 @@ def _select_recursive(parent_paths, dir_only, follow_symlinks):
     if follow_symlinks is None:
         follow_symlinks = False
     for parent_path in parent_paths:
-        paths = [parent_path]
+        paths = [parent_path._make_child_relpath('')]
         while paths:
             path = paths.pop()
             yield path