vfs_shadow_copy2: Use VFS interface to derive mount point

vfs_shadow_copy2: Use VFS interface to derive mount point

shadow_copy2_find_mount_point() does direct stat() calls locally while
trying to automatically detect the mount point. This cannot be always
true as there are virtual file systems like CephFS, GlusterFS etc.
without their share path locally available on the system. Instead use
the VFS interface to make the stat calls hit the underlying file system
irrespective of their local presence in the system.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15797

Signed-off-by: Anoop C S <anoopcs@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Reviewed-by: John Mulligan <jmulligan@samba.org>
Autobuild-User(master): Anoop C S <anoopcs@samba.org>
Autobuild-Date(master): Fri Feb  7 06:23:12 UTC 2025 on atb-devel-224

(cherry picked from commit c7d0adade09fa264201a125b28dd76c163451260)