Adds an exception so that the key-binding `control + Tab` does not get
duplicated as `command + Tab` on macOS because this is a global system
shortcut for the app switcher.
The key-binding `command + Tab` was shown for the operators “Toggle
Graph Editor“ and “Toggle Dope Sheet” in Dope Sheet and Graph Editor,
but only `control + Tab` actually worked.
Differential Revision: https://developer.blender.org/D10304
