[polari] (8 commits) ...cleanup: Use class getters instead of globals

[Gitlab Administrative User <gitlab src gnome org>]

Summary of changes:

  d546070... cleanup: Use Array.includes() to check for element existenc (*)
  caa067a... cleanup: Replace more plain objects with Maps (*)
  8abb0ed... cleanups: Remove unused imports (*)
  e8d14c6... cleanup: Regroup imports (*)
  7501530... cleanup: Import classes directly where it makes sense (*)
  0ab064a... cleanup: Make singleton classes public (*)
  ad43c20... cleanup: Use class methods for singleton pattern (*)
  e611aa3... cleanup: Use class getters instead of globals (*)

(*) This commit already existed in another branch; no separate mail sent