fs: Export in_group_or_capable()

Export in_group_or_capable() as a VFS helper function.

Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
Link: https://lore.kernel.org/r/20240620032335.147136-1-youling.tang@linux.dev


Signed-off-by: Christian Brauner <brauner@kernel.org>