xfs: support xrep_require_rtext_inuse on zoned file systems

Space usage is tracked by the rmap, which already is separately
cross-referenced.  But on top of that we have the write pointer and can
do a basic sanity check here that the block is not beyond the write
pointer.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>