Generate by using diff apply

[greggman]

In this version of generate.mjs we assume there is a file ./generated/index-temp.d.ts
that was created by calling bikeshed, applying our patches, and calling prettier
in the previous commit. This should give us the diff needed to take our generated file
to the current dist state.

We then generate a current bikeshed-fixup-prettier generated/index-temp.d.ts.
We copy that to generated/index.d.ts and apply the previous patch. If it applies
it should have just the new changes from index.bs

wdty? too brittle?

[greggman]

thoughts:

I think, if you wanted to add new comments you'd just add them to dist/index.d.ts. They'd get included next time. If the patch doesn't apply you'll get an unchanged generate/index.d.ts like you used to get. You can still compare and update dist/index.d.ts manually. I don't think you need to do anything else. You do need to commit generated/index-temp.d.ts each time.