DO NOT MERGE Incremental inliner

**Do not merge this PR yet**, it is obviously in a very rough state.

But now the algorithm should be complete enough that things won't change much anymore, except cleanups. So I'm posting it for the eager interested reader.
Only trigger notifications when an *inlineable* something has changed/disappeared/been added. I don't think it is possible, but I wish it was, so I kept this to remind myself I should keep thinking to see if I find a way to make this possible.