Add gem rbs collection manager

[pocke]

This PR introduces rbs collection subcommand to manage 3rd party RBSs.

Usage

See the added document, collection.md.

Example

I tried introducing rbs collection to my repository, rbs_rails. pocke/rbs_rails#187
It works well 😄

Next Steps

This PR is the first step, so there are remaining works. I'll do them in other PRs.

Support this feature by TypeProf and Steep

All rbs sub-command supports this feature, for example, rbs validate automatically loads RBSs from rbs_collection.yaml if the file exists. But TypeProf and Steep don't support it.

I'll do it soon 🚀 I guess it is an easy task.

Resolve stdlib dependencies

Currently rbs collection command resolves dependencies with Gemfile.lock. So it has a limitation that it can't resolve stdlib dependencies.

For example, pathname is a default gem, so we don't write add_runtime_dependency 'pathname' in order to use the library in a gem. Then a Gemfile.lock doesn't contain pathname even if the dependency actually depends on pathname library.

We need another approach to resolve stdlib dependencies.
We, soutaro, mame, and I, discussed the topic in closed meetings. We are considering introducing a meta file to describe stdlib dependencies for RBS repository, like manifest.yaml.

For example:

# ruby/gem_rbs_collection/gems/activesupport/6.0/manifest.yaml
dependencies:
  - name: pathname
  - name: logger
    version: 1.4 # Can specify a version (optional)
  - name: mutex_m
  # ...

Update individual gems

Currenly rbs collection update command only supports updating all gems. But I can easily imagine it is too loose. We'll want to update specific gems like we usually do bundle update rails csv nokogiri in Bundler.
I'll allow rbs collection update to take gem names as arguments, like rbs collection update rails csv nokogiri

Without Gemfile.lock mode

Currently rbs collection command assumes Gemfile.lock existence. I guess it may need no Gemfile.lock mode for a project without Bundler or Gemfile.lock is not committed.

Design document

I wrote a design document at the beginning of this PR. I think there are many differences since the doc. It looks obsolete.
https://pocke.kibe.la/shared/entries/3665a009-e229-4e56-a92b-c0743f7a49fe

[soutaro]

👍