Added missing `dispose()` for some disposable objects in Flutter

Missing calls to 'dispose()' are added for some disposable objects. For example, ContextMenuController did not dispose OverlayEntry, and EditableTextState did not dispose TextSelectionOverlay.

If some other code also invokes 'dispose()' for the object, and the object is protected from double disposal, the second 'dispose()' fails with the following error message:

Once you have called dispose() on a <class name>, it can no longer be used.

The convention is that the owner of an object should dispose of it.

This convention was broken in some places: owners were not disposing the disposable objects. The issue was fixed by adding a call to dispose(). However, if the object is protected from double disposal, this can cause failures when running in debug mode and dispose() is called elsewhere on the object.

If you encounter the following error, update your code to call dispose() only in cases when your code created the object.

Once you have called dispose() on a <class name>, it can no longer be used.

Code before migration:

x.dispose();

Code after migration:

if (xIsCreatedByMe) {
  x.dispose();
}

To locate the incorrect disposal, check the call stack of the error. If the call stack points to dispose in your code, this disposal is incorrect and should be fixed.

If the error occurs in Flutter code, dispose() was called incorrectly the first time.

You can locate the incorrect call by temporary calling print(StackTrace.current) in the body of the failed method dispose.

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