Always correct binding to multiline

[vinistock]

Trying to auto-correct callback conditionals can produce incorrect code if the method used inside is private. E.g.:

class Article
  # If we simply add `T.bind(self, Article).valid?` here, we get an error because valid? is private
  before_create :do_something, if: -> { valid? }

  private

  def valid?
    true
  end
end

Therefore, the only way of safely making these corrections is by always correcting to multi-line.

I also had to fix a documentation example which was breaking rake, so that I could re-generate the documentation.

Note
We had discussed changing the purpose of this cop to add the T.bind into any arbitrary method that we could specify via configuration. However, the place we need to insert the T.bind is different for certain types of methods.

E.g.:

# in this case, the block is the actual block argument
setup do
  T.bind(self, MyTest)
end

# in this case, the block is captured inside a hash options parameter and the actual block is a completely different argument
before_action if: -> { should_do_it? } do
end

If you have any ideas of how we could make this configurable and generic, please let me know. But my suggestion would be to have a different cop for regular blocks and this one remains for callbacks only.