Introduce RBS + Steep

[klaustopher]

Playing around with adding type signatures. Let's see where this goes

Tasks

• Introduce RBS, Stepp and rbs_rails
• Create needed config files
• Generate stuff for rails models (fb496a3)
• Generate stuff for a bunch of other files using rbs prototype rb ...
• Fix all errors or find a way to mark them as "okay" for now
• Add a GitHub action that runs steep
• Add a GitHub action that automatically updates RBS from gems for dependabot PRs (along the lines of https://github.com/klaustopher/pddln/blob/a09473a94e8553ff079ae5b061c7749920a9dc3f/.github/workflows/update-rbi.yml)
• Add a lefthook to run steep check as a before commit hook

Notes

• The repository at https://github.com/ruby/gem_rbs_collection seems to have quite a few outdated definitions for gems. Half of rails is still stuck at 6.0. There seems to be a project out there thatt tries to make a better generator than what is included in rbs collection: https://github.com/ksss/orthoses
• The meta-tags gem we use ships with definitions, that cause a problem. There is an issue ([error] Cannot find type '_ActionViewBase' from Steep kpumuk/meta-tags#253), but this is pretty stale. It seems there is currently no way to ignore known problems in the type checker. Investigating further

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Implements https://community.openproject.org/work_packages/47208

[klaustopher]

Links:

• https://evilmartians.com/chronicles/climbing-steep-hills-or-adopting-ruby-types
• https://github.com/ruby/typeprof/blob/master/doc/doc.md