feat(eslint-plugin): added new rule typedef

[JoshuaKGoldberg]

Adds the equivalent of TSLint's typedef rule.

Closes #558.

[bradzacher]

A few questions for you.
Had a quick eyeball of the rule code and it looks okay. I'll have a deeper look after these questions

[Shinigami92]

I really love the TSLint typedef rule and I cant migrate to eslint without the support of this rule. This said, I have one proposal what can improve typedef. Let us decide which option throws a warning and which throws an error -> so with this CI/CD can fail only on some of the options.

[bradzacher]

@Shinigami92 - this is not possible - eslint only allows for a single error level for a rule. Either it's all a warning, or it's all an error.

[Shinigami92]

Ok :/ sad but ok

[Shinigami92]

TSLint currently introduces a new option variable-declaration-ignore-function
palantir/tslint#2654

[bradzacher]

as mentioned, remove arrowCallSignature and callSignature from the rule.
document that users should instead use explicit-function-return-type.

Correct me if I'm wrong here - but looking at the options, I don't think that it needs to access parserServices at all - it's just checking for missing AST nodes. So if I'm not wrong, please remove the dependency on the parser services.

[codecov]

Codecov Report

Merging #581 into master will increase coverage by 0.01%.
The diff coverage is 96.66%.

@@            Coverage Diff             @@
##           master     #581      +/-   ##
==========================================
+ Coverage   94.45%   94.47%   +0.01%     
==========================================
  Files         111      112       +1     
  Lines        4690     4720      +30     
  Branches     1291     1306      +15     
==========================================
+ Hits         4430     4459      +29     
  Misses        150      150              
- Partials      110      111       +1

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/index.ts	100% <100%> (ø)	⬆️
packages/eslint-plugin/src/rules/typedef.ts	96.55% <96.55%> (ø)