btrfs: verify "btrfs filesystem defragment -c" behavior

btrfs: verify "btrfs filesystem defragment -c" behavior

Despite the regular file defragging, "btrfs filesystem defragment"
provides an option, -c, to convert all data extents (except holes
and preallocated ranges) to a new compression algorithm.

The special behavior here is, unlike regular defrag which is not
going to touch extents which are adjacent to preallocated/hole
ranges, with -c, all non-hole/non-preallocated extents should be
defragged and converted to the new compression algorithm.

This test case will ensure the old behavior is properly kept.

Currently both old kernels (v5.15 and older) and newer kernel with
refactored defrag (v5.16 and newer) can pass the tests.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>