Type cleanup

1. Remove a bunch of unnecessary explicit type declarations. Most notably, type inference for mapped array destructuring has worked correctly in the last few releases of typescript, so events don't need to explicitly type their actors.
2. Fix various type errors.
3. Clean up some unnecessary @ts-ignore directives (some were workarounds that could be removed, or problems that had already been fixed, and others were easily fixed).

Resyncing first. Big merge and all that.

merged

mentioned in commit 7a69a43f

mentioned in issue #3662 (closed)