Extract logic of detecting a Stapler view into extension point

[duemir]

• Simple predicated that test the PsiFile to tell if it is one of view types
  • Declared as Extension Point
• Example of optional extension implementation that only enabled when optional Groovy plugin dependency is installed.

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

This is more of an example of how to create an Extension Point. Not sure if this functionality needs an extension point exactly.