btrfs: test a case with compressed send stream and a shared extent

btrfs: test a case with compressed send stream and a shared extent

Test that if we have a snapshot with a compressed extent that is partially
shared between two files, one of them has a size that is not sector size
aligned, we create a v2 send stream for the snapshot with compressed data,
and then apply that stream to another filesystem, the operation succeeds
and no data is missing. Also check that the file that had a reference to
the whole extent gets two compressed extents in the new filesystem, with
only one of them being shared (reflinked).

This tests a recent patch that landed in kernel 6.1-rc7:

  a11452a3709e ("btrfs: send: avoid unaligned encoded writes when attempting to clone range")

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>