This is mostly just a follow up to #6342.
`prefer-optional-chaining` was turned on and fixed in every location it
complained in. The transformed function [0] looks expensive from a
glance but from skimming through the replaced sites it doesn't appear
to be ran in any important place, so it should be OK.
The linter improvements are:
- Increase linter performance
- Make `full-lint` and `lint` write to different caches so we
avoid overwriting their caches since they're different configs
- Change husky's hook to `npm run lint` so as to write to the
same cache
- Remove `@typescript-eslint/eslint-plugin-tslint` which is
essentially a wrapper to TSLint because the rules aren't worth
running another linter
- Convert `.eslintrc.json` and `.eslintrc-syntax.json` to two spaces
rather than four tabs to respect PS' `.editorconfig`
- Rename `fulllint` to `full-lint` to ease spelling it
[0] - https://pastie.io/mmtxpf.js (prettified)
