chore: add explicit-module-boundary-types lint rule

[SimenB]

Summary

I've found that type errors can be quite hard to understand when there are many layers of inference between the actual source of the type error and where it shows up as an actual type error. By typing all exported functions within a single file, any type error should at least have its origin within one file, instead of having to dig though multiple layers.

Rule docs: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/explicit-module-boundary-types.md

One annoying thing is that it doesn't recognise any as a type, which is somewhat painful in certain circumstances (like for matchers in expect)

Test plan

Green CI

[thymikee]

That's a lot of typings :o but sounds good. This is something that Flow started to do recently, but mostly for perf reasons I think

[codecov-io]

Codecov Report

Merging #9539 into master will increase coverage by 0.02%.
The diff coverage is 88.34%.

@@            Coverage Diff             @@
##           master    #9539      +/-   ##
==========================================
+ Coverage   65.03%   65.05%   +0.02%     
==========================================
  Files         283      283              
  Lines       12113    12120       +7     
  Branches     3000     3004       +4     
==========================================
+ Hits         7878     7885       +7     
  Misses       3597     3597              
  Partials      638      638

Impacted Files	Coverage Δ
packages/jest-watcher/src/PatternPrompt.ts	0% <ø> (ø)	⬆️
packages/jest-util/src/createDirectory.ts	0% <ø> (ø)	⬆️
...ges/jest-core/src/getNoTestFoundPassWithNoTests.ts	100% <ø> (ø)	⬆️
...es/jest-watcher/src/lib/formatTestNameByPattern.ts	84.21% <ø> (ø)	⬆️
packages/babel-plugin-jest-hoist/src/index.ts	0% <ø> (ø)	⬆️
packages/jest-jasmine2/src/jasmineAsyncInstall.ts	0% <ø> (ø)	⬆️
...ages/jest-worker/src/workers/ChildProcessWorker.ts	90% <ø> (ø)	⬆️
packages/jest-runner/src/testWorker.ts	0% <ø> (ø)	⬆️
packages/pretty-format/src/collections.ts	98.48% <ø> (ø)	⬆️
packages/jest-jasmine2/src/reporter.ts	59.52% <ø> (ø)	⬆️
... and 96 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 481077b...92199bb. Read the comment docs.

[SimenB]

Found a bug with this rule, so will need another pass when that's fixed 😅 typescript-eslint/typescript-eslint#1583

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.
Please note this issue tracker is not a help forum. We recommend using StackOverflow or our discord channel for questions.