Import type definitions with `rbs prototype runtime`

[Masataka Pocke Kuwabara]

Now we have only a few type definitions.
So I think it is a good idea to import type definitions with rbs prototype runtime.

I tried generating rbs files for Active Record, and got the following rbs.
https://gist.github.com/pocke/2ed43fdbc11fa0df72d098a65127fea4

But we still have several problems to merge the rbs to this project.

• The RBS is generated with Rails with the master branch because it needs several patches.
  • So we need to backport the patches to v6 and re-generate the RBS.
• We already have a few types under assets/sig/ directory, so we need to merge them.
• The generated RBS is not tested. I just generated and did nothing else. So it probably doesn't work well.
• It only contains Active Record, but we need other libraries such as Active Support.
  • But we can introduce the generated rbs step by step.

[Masataka Pocke Kuwabara]

I haven't tried yet, but I guess rbs prototype rb is also useful.
Maybe we can combine rbs prototype rb and rbs prototype runtime.

[Masataka Pocke Kuwabara]

almost done