Bug 1941140 - Make TextControlState::UnbindFromFrame clean up controllers if and only if they are exist r=edgar

`HTMLInputElement::GetControllers()` and `HTMLTextAreaElement::GetControllers()`
initializes their controllers before returning the `nsIControllers` instance
[1][2].  Typically, they are initialized at creating their `TextEditor`
instance is initialized [3].  A `TextEditor` for an `HTMLInputElement` is
initialized when it gets focus first time after the `nsTextControlFrame` is
created [4][5].  Therefore, when `TextControlState::UnbindFromFrame` is called,
the element may not have controllers yet.  So, the elements should have simple
getters of their controllers and `UnbindFromFrame` should use them instead.

1. https://searchfox.org/mozilla-central/rev/eb80f267aabbf90ac66ebbed77b6d33592eb2be0/dom/html/HTMLInputElement.cpp#5658-5660
2. https://searchfox.org/mozilla-central/rev/eb80f267aabbf90ac66ebbed77b6d33592eb2be0/dom/html/HTMLTextAreaElement.cpp#502-503
3. https://searchfox.org/mozilla-central/rev/eb80f267aabbf90ac66ebbed77b6d33592eb2be0/dom/html/TextControlState.cpp#1826-1827,1832,1837-1838,1857-1858
4. https://searchfox.org/mozilla-central/rev/eb80f267aabbf90ac66ebbed77b6d33592eb2be0/layout/forms/nsTextControlFrame.cpp#447
5. https://searchfox.org/mozilla-central/rev/eb80f267aabbf90ac66ebbed77b6d33592eb2be0/dom/html/TextControlState.cpp#1640-1641,1655-1656

Differential Revision: https://phabricator.services.mozilla.com/D234307

dom/html/HTMLInputElement.cpp

@@ -5689,7 +5689,7 @@ nsIControllers* HTMLInputElement::GetControllers(ErrorResult& aRv) {
     }
   }
 
-  return mControllers;
+  return GetControllersWithoutCreation();
 }
 
 nsresult HTMLInputElement::GetControllers(nsIControllers** aResult) {