bcachefs: Indirect inline data extents

bcachefs: Indirect inline data extents

When inline data extents were added, reflink was forgotten about - we
need indirect inline data extents for reflink + inline data to work
correctly.

This patch adds them, and a new feature bit that's flipped when they're
used.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>