feat(envs API) - Support custom dep detectors for envs

[Jinjiang]

Proposed Changes

• Expose detectors() to the new env interface.
• Revamp the implementation of the precinct and detector hook.
• Extend the interface DependencyDetector by adding an optional type member, which is better to be further processed rather than ext member.

Something needs to pay attention to:

1. I didn't find any places to consume precinct.ast. Here I just passed the relevant test cases.
2. I didn't find any external places to call precinct() except in precinct.paperwork(). Here I just passed the relevant test cases. And since those 2 functions are not nested anymore, I skipped the case: paperwork -> when given detective configuration -> still does not filter out core module by default.

[davidfirst]

@Jinjiang , Great job with this PR! :)

Regarding the points you mentioned:

1. It's populated in precinct index.ts file ast = walker.parse(content); and it's consumed in filling-cabinet/index.ts file: const ast = options.ast || options.content; to determine the js type (amd/commonjs/es6).
   Not sure how important it is, because seems like this is for optimization only to not re-parse. If the ast is not there, it uses the content and then later on parses it. Also, we probably currently treat all JS as ES6, so maybe we can even remove more unneeded stuff there later on.

2. Makes sense. Yes, I believe it gets called only from paperwork and it's fine to skip that test (or even delete it).

[GiladShoham]

What possible values are for this?
if it's general string, we should improve the comment above it to explain what it is

[Jinjiang]

This type is what precinct() previously receives as the second argument. Also, it's what the previous getType() returns in paperwork(). I added this field into the detector interface to combine the 2 steps directly.

The previous implementation has 2 steps: 1) get the type from the ext, 2) get detective from the type.

Sometimes ext names and types are not 1:1 matched. For example, .ts and .tsx both match the type ts.

For custom env detectors, I think it's also a good practice for detector authors to specify what type of files it belongs to.

And I updated the code comment a little bit. What do you think now? :-)