generic: fallocate against a file range with a mix of holes and extents

generic: fallocate against a file range with a mix of holes and extents

Test that if we call fallocate against a file range that has a mix
of holes and written extents, the fallocate succeeds if the
filesystem has enough free space to allocate extents for the holes.

This test currently fails on btrfs and is fixed by a patch that has the
following subject:

    "btrfs: only reserve the needed data space amount during fallocate"

The test also fails on xfs, and after some discussion with Darrick,
it seems it's due to technical reasons that would require a
significant effort to xfs's implementation, and at the moment there
isn't enough motivation to do such change. The relevent thread is at:

    https://lore.kernel.org/linux-btrfs/20220315164011.GF8241@magnolia/

Therefore the test is intentionally skipped on xfs only. Ext4 and
f2fs pass this test.

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