Enable some more @typescript-eslint rules

[pjonsson]

What this PR does

Enable some more @typescript-eslint rules.

These rules seem worthy of keeping enabled so more of these issues don't get into the code base. I don't have a strong opinion that all of them have to be enabled, so if some rule is contentious, just let me know and I'll drop that commit so the rest of the PR can get merged.

Test me

Run yarn gulp lint and see that the linter passes.

Checklist

• [ ] There are unit tests to verify my changes are correct or unit tests aren't applicable (if so, write quick reason why unit tests don't exist)
• [ ] I've updated relevant documentation in doc/.
• [ ] I've updated CHANGES.md with what I changed.
• [X] I've provided instructions in the PR description on how to test this PR.

[na9da]

Looks good to me too. Thanks @pjonsson!