xfs_db: introduce the 'fsmap' command to find what owns a set of fsblocks

xfs_db: introduce the 'fsmap' command to find what owns a set of fsblocks

Introduce a new 'fsmap' command to the fs debugger that will query the
rmap btree to report the file/metadata extents mapped to a range of
physical blocks.

[dchinner: xfs_rmap_query_range -> libxfs_rmap_query_range]

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>