Add new config arguments_or_slashes to Rails/FilePath

[tejasbubane]

Config to just check for usage of File.path, but doesn't care about arguments to Rails.root.join

---

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.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.
• 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.

[koic]

I think the concept is good 👍 However I doubt the addition of the new parameter EnforcedStyle: arguments_or_slashes. I think this cop should probably be updated to accept multiple EnforcedStyle configuration using AllowMultipleStyles: true.

# .rubocop.yml
Rails/FilePath:
  EnforcedStyle:
    - slashes
    - arguments

Refer: rubocop/rubocop#6649

[tejasbubane]

@koic Looks like rubocop does not support multiple styles for EnforcedStyle yet - CI error.

[koic]

Yup. About implementation should investigate the cause of the error and resolve it. I haven't reached the cause yet. AllowMultipleStyles provides new representation option for user, but it is a relatively new parameter and needs to be grown when something is missing.