RuboCop: Improve performance

What does this MR do and why?

This MR improves performance of RuboCop - specially it reduces the runtime of rubocop job by ~24 % (from 3359 seconds to 2553 seconds 🚀).

See #377469 for more details and profiling information.

It also adds a new utility bin/rubocop-profile to profile bundled RuboCop.

How to set up and validate locally

# Run full scan with cold cache
rm -fr tmp/rubocop_cache && time bundle exec rubocop --parallel

# Or run a subset of files
rm -fr tmp/rubocop_cache && time bundle exec rubocop {spec,app}/models/project*

# Profile yourself!
bin/rubocop-profile {spec,app}/models/project*
stackprof tmp/stackprof.dump

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.