Don't register RSpec/DescribedClass offenses within Data.define blocks

[lovro-bikic]

Fixes #2086.

Changes RSpec/DescribedClass so it doesn't register offenses within a Data.define block. Previously, this:

RSpec.describe Demo do
  let(:data) { Data.define(:foo) { include Demo } }
end

would have been an offense (with autocorrection to include described_class, which would raise an error because described_class isn't available within that block). With the patch, this code no longer produces an offense.

---

Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Updated documentation.
• Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

If you have created a new cop:

• Added the new cop to config/default.yml.
• The cop is configured as Enabled: pending in config/default.yml.
• The cop is configured as Enabled: true in .rubocop.yml.
• The cop documents examples of good and bad code.
• The tests assert both that bad code is reported and that good code is not reported.
• Set VersionAdded: "<<next>>" in default/config.yml.

If you have modified an existing cop's configuration options:

• Set VersionChanged: "<<next>>" in config/default.yml.

[ydah]

Thank you!

[pirj]

Thank you!