- Rename action_cable/*.coffee -> *.js
- Move app/assets/javascripts/* -> app/javascript/*
- Rename action_cable.js.erb -> action_cable/index.js.erb
Renaming the extension to .js is in preparation for converting these
files from coffeescript to ES2015.
Moving the files to app/javascript and putting the entry point in
index.js.erb changes the structure of ActionCable's javascript to match
the structure of ActiveStorage's javascript.
(We are doing the file moving and renaming in a separate commit to
ensure that the git history of the files will be preserved - i.e. git
will track these as file renames rather than unrelated file
additions/deletions. In particular, git blame will still trace back to
the original authorship.)
