Move signature diffing into dedicated Signature.diff methods.
Review Request #10304 — Created Nov. 2, 2018 and submitted
This introduces new
diff()methods on signatures that focus on diffing
the content against another signature of the same type. These are used
by the main
Diffclass to perform the diffing (though in time that
class may disappear).
By splitting this out, the diffing logic becomes a lot more readable,
and we'll be able to use it for more fine-grained diffs and evolutions
down the road.
All unit tests pass.