[Review Only] JS Code Hints: Remember timed out files, notify user

@dangoor 

I pushed this interim branch for you to take a look. This works for some code paths.

TODO:
- [x] bug: `isFileExcludedInternal()` not called on all code paths (cannot repro, maybe confused similar file names)
- [x] implement notification dialog
- [x] don't exclude file currently being edited
- [x] convert pref to project scope?
- [x] remove `console.log()` statements
- [ ] rebase this branch

We want these exclusions to be separate from user exclusions so they don't show up in UI list, right? These are orthogonal be cause we want to check these exclusions in addition to any other exclusions that the user selects.