Additional rules to consider

The following two rules have popped up a few times in various other package's custom eslint configs, they might be worth adding to core:

```
// There's a TypeScript-specific version of this rule;
// we disable the generic one, because it thinks imported types are unused
// when they're not:
"no-unused-vars": "off",
"@typescript-eslint/no-floating-promises": "error",
```