Merge PR #24068 into master

* refs/pull/24068/head:
	mds: rename {CDir,Migrator}::cache to mdcache
	mds: make MDSCacheObject::is_ambiguous_auth() virtual
	mds: make sure rename old inode's parent dirfrag is projected.
	mds: track projected inode/fnode in Mutation
	mds: use smart pointer to manager CDir::fnode
	mds: use smart pointer to manage CInode::{inode,xattrs,old_inodes}
	osdc/Filer: make layout pointer const

Reviewed-by: Patrick Donnelly <pdonnell@redhat.com>