Modify `Rails/Pluck` to ignore `map/collect` when used inside blocks to prevent potential N+1 queries

This PR modifies the Rails/Pluck cop to ignore map/collect when used inside blocks to prevent potential N+1 queries.

When the receiver's relation is not loaded and pluck is used inside an iteration, it can result in N+1 queries. This happens because pluck executes a database query on every iteration when the relation is not loaded.

Example

users = User.all
5.times do
  users.map { |user| user[:id] } # Only one query is executed
end

users = User.all
5.times do
  users.pluck(:id) # A query is executed on every iteration
end

users = User.all
users.load

5.times do
  users.pluck(:id) # Since the records are loaded, only one query is executed
end

As shown above, replacing map/collect with pluck in such cases can degrade performance due to the N+1 queries. To prevent this, it is better to ignore map/collect when used inside an iteration.

Challenge

Since Ruby has numerous methods for performing iterations, it is difficult to list all of them. Therefore, this PR assumes that map/collect used inside blocks are likely part of an iteration and ignores offenses.

Before submitting the PR make sure the following are checked:

[x] The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
[x] Wrote good commit messages.
[ ] Commit message starts with [Fix #issue-number] (if the related issue exists).
[x] Feature branch is up-to-date with master (if not - rebase it).
[x] Squashed related commits together.
[x] Added tests.
[x] Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
[x] 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.

rubocop / rubocop-rails

Modify `Rails/Pluck` to ignore `map/collect` when used inside blocks to prevent potential N+1 queries #1388

Example

Challenge