xfs: use interval query for rmap alloc operations on shared files

xfs: use interval query for rmap alloc operations on shared files

Source kernel commit: ceeb9c832eeca5c1c2efc54a38f67283ccb60288

When it's possible for reverse mappings to overlap (data fork extents
of files on reflink filesystems), use the interval query function to
find the left neighbor of an extent we're trying to add; and be
careful to use the lookup functions to update the neighbors and/or
add new extents.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>