kernel/fs: Introduce check_write_stat_permissions utility method.

Like check_access_permissions() but for write_stat() hook instead
of access().

Basic logic copied from BFS, but with the UID/GID logic rewritten
to better conform to behavior on other OSes: notably, we allow
chown() requests that keep the UID the same to go through, same
as Linux seems to, which should fix #19666. We now also validate
that the GID is one of the current team's groups.

headers/private/fs_shell/fssh_api_wrapper.h

@@ -950,6 +950,7 @@
 #define get_vnode_removed			fssh_get_vnode_removed
 #define volume_for_vnode			fssh_volume_for_vnode
 #define check_access_permissions	fssh_check_access_permissions
+#define check_write_stat_permissions fssh_check_write_stat_permissions
 #define read_pages					fssh_read_pages
 #define write_pages					fssh_write_pages
 #define read_file_io_vec_pages		fssh_read_file_io_vec_pages