xfs_repair: convert regular rmap repair to use in-memory btrees

xfs_repair: convert regular rmap repair to use in-memory btrees

Convert the rmap btree repair code to use in-memory rmap btrees to store
the observed reverse mapping records.  This will eliminate the need for
a separate record sorting step, as well as eliminate the need for all
the code that turns multiple consecutive bmap records into a single rmap
record.

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