New: Add ESLint#getRulesMetaForResults() (refs #13654)

[nzakas]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[x] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

Added the ESLint#getRulesMetaForResults() method. This method was proposed as ESLint#getRulesMetaForReport() but that wording was incorrect in the RFC because it's CLIEngine that return a report while ESLint returns an array of results, so I updated the name to match that reality.,

I chose to return an object so that the rulesMeta passed to formatters is the same format rather than returning a map.

This part of the RFC is non-breaking, which is why I chose to create a separate PR for it.

Is there anything you'd like reviewers to focus on?

Does this implementation match everyone's expectations?

[mdjermanovic]

LGTM aside from the comments about the documentation.

Does this implementation match everyone's expectations?

I'd guess this covers all use cases where CLIEngine#getRules() was used, but can't be sure.

Assuming that it covers all use cases, I think it makes sense to require the results argument, as it clarifies this method and emphasizes that it should be called after ESLint#lintFiles()/ESLint#lintText().

[nzakas]

Docs have been updated. I think between use-at-your-own-risk builtinRules and this method, we are covering the majority of cases. We can always look at adding more methods if we find a gap.

[btmills]

LGTM. Just one fix to the docs, and I'll commit that inline if you don't see it by the time I'm ready to do the release so it can go out today.