Refactor controller architecture and multi-insert state

- Rename ControllerContext to ControllerMessageBus for clarity
- Switch ControllerBase to use SingletonRaised
- Replace MarkEventsMixin with MarkerManager for multi-cursor editing
- Add populate_popup event support for source view context menus
- Remove unused swap file events
- Moved JSON prettify feature to plugin
- Fix event name: "removed_file" -> "remove_file"

src/libs/singleton_raised.py

@@ -15,15 +15,15 @@ class SingletonError(Exception):
 T = TypeVar('T', bound='SingletonRaised')
 
 class SingletonRaised:
-    _instance = None
+    __instance = None
 
     def __new__(cls: Type[T], *args: Any, **kwargs: Any) -> T:
-        if cls._instance is not None:
+        if cls.__instance is not None:
             raise SingletonError(f"'{cls.__name__}' is a Singleton. Cannot create a new instance...")
 
-        cls._instance = super(SingletonRaised, cls).__new__(cls)
-        return cls._instance
+        cls.__instance = super(SingletonRaised, cls).__new__(cls)
+        return cls.__instance
 
     def __init__(self) -> None:
-        if self._instance is not None:
+        if self.__instance is not None:
             return