[Fix #7647] Handle numblock

[hanachin]

Fix #7647

# 7647/.rubocop.yml
AllCops:
  TargetRubyVersion: 2.7

#!/usr/bin/env ruby
# frozen_string_literal: true

# 7647/test.rb

def hello(meaning)
  spliters = [',', '.', '!']
  spliters.each { meaning = meaning.split(_1).first }
  meaning.delete('"').strip.gsub("\r\n", '; ')
end

$ pwd
/home/sei/src/github.com/rubocop-hq/rubocop
$ cd 7647
$ ../exe/rubocop
Inspecting 1 file
.

1 file inspected, no offenses detected

---

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.

[pocke]

Thanks for your pull request 👍

We still need to apply more changes to make cops to work for numblock even if we merge this pull request. Because the cops will just ignore numblock.
I created an issue for the problem. #7666 See the issue for more detail.

I think this pull request is acceptable without more support for numblock. We can work for #7666 with another pull request.
This bug is critical for Ruby 2.7 users. But #7666 is a smaller problem than the bug. So I think we can fix the cops after this pull request.

[koic]

As @pocke mentions at #7665 (comment), this patch doesn't solve all known issue of numblock. So the Handle numblock seems a bit broad sense to me. What about alternatives like the following message focused on resolving the error?

-* [#7647](https://github.com/rubocop-hq/rubocop/issues/7647): Handle numblock. ([@hanachin][])
+* [#7647](https://github.com/rubocop-hq/rubocop/issues/7647): Fix an `undefined method on_numblock` error when using Ruby 2.7's numbered parameters. ([@hanachin][])

[pocke]

👍

[koic]

Thanks!