Document that CollisionShape(2D) instances share a resource, and that 'Local to Scene' can override this

[Error7Studios]

Your Godot version:
3.2.4 RC 2

Issue description:
It isn't obvious that instanced CollisionShape nodes will share a resource, or why.
The Make Sub-Resources Unique checkbox seems to have no effect on this issue.
Something like this should probably be added at the top of the CollisionShape and CollisionShape2D docs:

For performance reasons, all instanced CollisionShape(2D) nodes share the same resource.
To override this and create unique resources for each instance, check the Local to Scene box in the inspector.

Issues:
godotengine/godot#38066
https://www.reddit.com/r/godot/comments/ljd49i/instanced_objects_interact_as_one_object/
https://godotengine.org/qa/95271/give-unique-size-to-different-collisionshape2d-instances
godotengine/godot-proposals#317

URL to the documentation page (if already existing):
https://docs.godotengine.org/en/stable/classes/class_collisionshape.html
https://docs.godotengine.org/en/stable/classes/class_collisionshape2d.html

[samuel-walker]

Just to motivate this a bit – I just found this issue from Google and it helped me solve my problem! It seemed like a good idea to make a single character scene for a multiplayer game, and just instance one scene for each player. However, I was noticing the CollisionShape2D of multiple instanced character scenes were being animated together! I somehow forgot the resource would be shared. Mentioning this in the docs or tutorials as reminder for new users like me would be great.