get_maintainer: add ** glob pattern support

get_maintainer: add ** glob pattern support

Add support for the ** glob operator in MAINTAINERS F: and X: patterns,
matching any number of path components (like Python's ** glob).

The existing * to .* conversion with slash-count check is preserved.  **
is converted to (?:.*), a non-capturing group used as a marker to bypass
the slash-count check in file_match_pattern(), allowing the pattern to
cross directory boundaries.

This enables patterns like F: **/*[_-]kunit*.c to match files at any depth
in the tree.

Link: https://lkml.kernel.org/r/20260302103822.77343-1-teknoraver@meta.com
Signed-off-by: Matteo Croce <teknoraver@meta.com>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>