On the first request, ActionController::Base#action_methods computes
and memoized the list of available actions [1]. With this PR we move
this expensive operation into eager load step to reduce response time
of the first request served in production.

This also reduces the memory footprint when running on forking server
like Unicorn.

[1] https://github.com/rails/rails/blob/a3813dce9a0c950a4af7909111fa730a2622b1db/actionpack/lib/abstract_controller/base.rb#L66-L77