This change enables inline cache to work as expected with MergeOp by
supporting a new type of result, DiffResult, which enables results to be
specified as a specific ordered set of layers inside an image.
Previously, results could only be specified with a singe layer index,
which meant that they had to start at the image's base layer and end at
that index. That meant that merge inputs couldn't be specified as they
are often a subset of the image layers that don't begin at the base.
Signed-off-by: Erik Sipsma <erik@sipsma.dev>