[Fix #7433] User vs project exclusion inheritance

[deivid-rodriguez]

If there's a specific project configuration, we want the exclusions for the user configuration to be ignored, just like the rest of the configuration is ignored.

Note that this solution slightly changes behavior if people are running rubocop for within a subproject folder that resolves to a .rubocop.yml different from the one in the root folder. However, I believe that if people are doing this, they are probably using --ignore-parent-exclusion already, so it's not going to be an issue.

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.

[deivid-rodriguez]

There's an error which sounds like it's my fault. I'll have a look.

[deivid-rodriguez]

Ok, so I tried this on a real project and it did "break" my editor integration when inspecting vendored code.

• Without this PR, if I change a vendored file in a way that's not compliant with its own configuration, it will complain.
• With this PR, my editor will simply ignore vendored code (excluded from root configuration).

I believe it's debatable which behaviour is best, but I'll try to change this PR to be fully backwards compatible with the previous behaviour in this regard and add a regression spec.

[deivid-rodriguez]

Ok, I don't think I was testing this correctly. Turns out this PR is also correcting a very strange behaviour regarding vendored files.

The standard behavior of my editor rubocop integration is to ignore vendored files. That's unchanged with this PR.

However, if I put a ~/.rubocop.yml file in my home folder (with any content, as far as I can see), then my editor integration starts checking the vendored file for some reason 🤨. This PR also fixes that issue.

For what it's worth, my editor integration is https://github.com/dense-analysis/ale/, and the rubocop command run under the hood looks like: bin/rubocop --format json --force-exclusion --stdin /home/deivid/Code/activeadmin/vendor/bundle/ruby/2.7.0/bundler/gems/rubocop-1fe8dd1d8582/lib/rubocop.rb < /tmp/nvimchZ4vE/1/rubocop.rb.

[jonas054]

The changelog entry now needs to be moved up to the master (unreleased) section, but other than that the changes look good. 👍

[deivid-rodriguez]

@jonas054 Thanks!! I rebased this PR and moved the changelog entry.