[Fix #8582] Add new Layout/BeginEndAlignment cop

[koic]

Fixes #8582.

This PR adds Layout/BeginEndAlignment cop to solve the issue.

The following is an example:

% cat example.rb
foo = bar rescue "{}"

Before

The alignment was misaligned because begin was not awake.

% rubocop -a example.rb
(snip)

% cat example.rb
foo =
  begin
         bar
  rescue StandardError
    '{}'
       end

After

Awakened by begin, so aligned.

% rubocop -a example.rb
(snip)

% cat example.rb
foo =
  begin
    bar
  rescue StandardError
    '{}'
  end

I was first planning to add begin processing to Layout/EndAlignment cop.
However, Layout/EndAlignment cop with EnforcedStyleAlignWith: keyword (default) was not preferred code in the following:

longlonglonglonglonglonglonglonglong ||= begin
                                           do_something
                                         end

This style has been found to have very long line length with RuboCop's own code.

Therefore, since this PR would like to use EnforcedStyleAlignWith: start_of_line by default against foo ||= begin, this PR added the new cop.

# EnforcedStyleAlignWith: start_of_line (default)
longlonglonglonglonglonglonglonglong ||= begin
  do_something
end

This solution allows configuration with minimal impact on existing code.

It is configurable if user want to align to begin.

# EnforcedStyleAlignWith: begin
longlonglonglonglonglonglonglonglong ||= begin
                                           do_something
                                         end

This PR also makes Layout/RescueEnsureAlignment cop aware of new Layout/BeginEndAlignment cop's config to align rescue indents.

---

Before submitting the PR make sure the following are checked:

• 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.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[bbatsov]

I'm fine with proposed solution, but I think we need to update the descriptions of BeginEndAlignment and EndAlignment to make it clear why we have two cops and what exactly are their responsibilities. Even for me the current arrangement is slightly confusing, so I can imagine it'd be even more confusing for our casual users.

[koic]

Ah, exactly! I updated the docs.

[mobilutz]

Awesome cop. I always thought the default begin/end alignment was strange 😉