Support Prism as a Ruby parser

[koic]

Follow up rubocop/rubocop-ast#277

There are no changes to the implementation, but the required dependency version of RuboCop AST will be updated. It would be more rational than adding new dependency on gem 'rubocop-ast', '>= 1.31.1' in the Gemfile just to bump up the minor version.

RuboCop Minitest now ensures that RuboCop::AST::ProcessedSource used in tests is aware of parser_engine parameter.

Tests for RuboCop AST with Prism as the backend can be run as follows:

bundle exec rake prism_test

The above is the shortcut alias for:

PARSER_ENGINE=parser_prism bundle exec rake test

RuboCop works on Ruby versions 2.7+, but since Prism only targets parsing for Ruby 3.3+, internal_investigation Rake task will not be executed. This task is only run with the Parser gem, which can parse Ruby versions 2.0+.

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Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• 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.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• 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.