Add support for chained method calls in Rails/Presence

[vlad-pisanov]

Fixes #932

Enhance Rails/Presence to detect and autocorrect a common scenario where a method is invoked on the receiver when it's present?, and nil otherwise:

# bad
name.present? ? name.upcase : nil
name.blank? ? nil : name.upcase
name.upcase if name.present?

# good
name.presence&.upcase

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.

[vlad-pisanov]

this could be autocorrected, but looks wonky: a.presence&.[](1)

same with arithmetic operators, and multiple method calls

[ydakuka]

The cop works not only with nil as an operand, and there is a corresponding test example:

it 'registers an offense and corrects when `a.present? ? a : b`' do
  expect_offense(<<~RUBY)
    a.present? ? a : b
    ^^^^^^^^^^^^^^^^^^ Use `a.presence || b` instead of `a.present? ? a : b`.
  RUBY

  expect_correction(<<~RUBY)
    a.presence || b
  RUBY
end

However, your suggested implementation does not account for this case:

it 'does not register an offense' do
  expect_no_offenses(<<~RUBY)
    a.present? ? a.foo : b
  RUBY

  # expect_correction(<<~RUBY)
  #   a.presence&.foo || b
  # RUBY
end

or this one:

it 'does not register an offense' do
  expect_no_offenses(<<~RUBY)
    a.foo || b if a.present?
  RUBY

  # expect_correction(<<~RUBY)
  #   a.presence&.foo || b
  # RUBY
end