Port over docs and typings from mobject.py/vectorized_mobject to their OpenGL counterparts. (#2354)

* remove event-handling from opengl_mobject.py

* bring over docs for many functions

* add duplicate method

* port over def mobject.become

* add misc docs and docs for add/remove/add_to_back

* add __repr__ for opengl mobs

* rename instances of Mobject->OpenGLMobject

* expand functionality for OpenGLVGroup

* add override animations + docs for set default

* add typings for openglvmob

* port docs and add proportion_from_point

* remove override_animation stuff from opengl_mobject.py

* make proportion_from_point work

* add remainder of docs

* add docs for somewhat-duplicated classes

* replace VMob with OpenGLVmob

* run black

* remove unecessary imports

* minor cleanup

* run black and isort

* make add_background_rectangle consistent between cairo/opengl

* compatibility layer does not exist in opengl_mobs

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Author: hydrobeam

manim/mobject/mobject.py

@@ -1632,7 +1632,7 @@ def put_start_and_end_on(self, start, end):
 
     # Background rectangle
     def add_background_rectangle(
-        self, color: Colors = BLACK, opacity: float = 0.75, **kwargs
+        self, color: Optional[Colors] = None, opacity: float = 0.75, **kwargs
     ):
         """Add a BackgroundRectangle as submobject.