Add new Rails/IncludeViewHelper cop

[mathieugoedhart96]

Summary

Add a new Rails/IncludeViewHelper cop that disallows including view helper modules outside of view contexts.

View helpers (modules in the ActionView::Helpers namespace or following the *Helper naming convention) depend on the view context. Including them in controllers, models, jobs, etc. may cause methods to fail silently or raise errors because the view context is not present.

Modules in app/helpers are automatically included into all views by Rails. If shared behaviour is needed across multiple classes, it should be extracted into a concern under app/concerns instead. In controllers, the helpers proxy can be used to call helper methods.

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