Convert Action generator to use RubyClassFile

[cllns]

This builds on #284, which must be merged first.

Note that we can't get rid of the ActionContext yet because it's used in hanami/rspec.

It's hard to parse the changes for the spec file, but I was able to fix a specs where --skip-view was still generating a view

TODO:

• [x] Replace x.x.x with whatever version this will be included with
• [x] ~Backport view changes to #284~ Skipping since #284 was approved and this PR can be reviewed next