landlock: Move access types

landlock: Move access types

Move LANDLOCK_ACCESS_FS_INITIALLY_DENIED, access_mask_t, struct
access_mask, and struct access_masks_all to a dedicated access.h file.

Rename LANDLOCK_ACCESS_FS_INITIALLY_DENIED to
_LANDLOCK_ACCESS_FS_INITIALLY_DENIED to make it clear that it's not part
of UAPI.  Add some newlines when appropriate.

This file will be extended with following commits, and it will help to
avoid dependency loops.

Cc: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20250108154338.1129069-6-mic@digikod.net
[mic: Fix rebase conflict because of the new cleanup headers]
Signed-off-by: Mickaël Salaün <mic@digikod.net>