[Fix #12105] Adjust target ruby gem requirement matcher and version parsing to support multiple version constraints

[ItsEcholot]

This PR adjusts the gem_requirement matcher to support multiple version constraints if Gem::Requirement is used as a value for required_ruby_version in the gemspec. It also allows version constraints in Gem::Requirement where the string was frozen with .freeze.

More information can be found in the linked issue #12105.

Example which is now supported with this PR:

Gem::Specification.new do |s|
  s.required_ruby_version = Gem::Requirement.new(['>= 2.3.1'.freeze, '< 3.0.0'.freeze])
end

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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.

[koic]

Can you add a changelog entry?

[koic]

Thanks!