lint: custom lint rules

[justinmk3]

• ✅ introduce a way to write custom lint rules: https://github.com/aws/aws-toolkit-vscode/pull/4118
• implement these custom lint rules:
  • ✅ disallow .only() in tests https://github.com/aws/aws-toolkit-vscode/pull/950#discussion_r387819343
  • ✅ disallow direct use of console.log (use getLogger instead) https://github.com/aws/aws-toolkit-vscode/pull/5087
  • require awsToolkit.clock.setInterval/setTimeout/etc (instead of setInterval/setTimeout/etc), awsToolkit.clock.Date (instead of new Date() or Date.foo()) #2343
  • disallow backend Vue code in src/webviews/util.ts https://github.com/aws/aws-toolkit-vscode/pull/3868/files#diff-4fd67c2312884124b237854f76518a3833a94909984327434aeabc942974bb50
• other potential custom lint rules:
  • plugins/eslint-aws/lib/rules/no-localize-aws.ts in #1859
  • plugins/eslint-aws/lib/rules/no-mocha-arrows.ts in #1859

[JadenSimon]

https://github.com/aws/aws-toolkit-vscode/pull/1859 has the skeleton for custom linting rules Right now writing your own rules is kind of tough since you need to know a lot about the Typescript AST (or ES AST), though I'm sure we can write some easy abstractions for our use-cases.