Document that SeparationRayShape2D and SeparationRayShape3D can be used for stairs.

[theraot]

Your Godot version:

4.2.dev5

Issue description:

Apparently SeparationRayShape2D and SeparationRayShape3D can be used for stairs, which means these classes more useful than the proposed use case of "spears falling from the sky" suggests.

Personally the mention of "stairs" would have gotten me to try. As I'll proceed to do after posting this.

With that said, I believe the documentation could expand on this shapes work or are intended to work beyond mentioning another use case.

These links support the idea that this is an use case of these shapes:

• third party: https://twitter.com/passivestar_/status/1707381014509519094
• first party: Add automatic smooth stairs step-up and step-down for KinematicBody using move_and_slide() godot-proposals#2751 (comment)

Apparently "It was designed for this very use case" (source), but that didn't make it to the documentation.

URL to the documentation page:

• https://docs.godotengine.org/en/stable/classes/class_separationrayshape2d.html
• https://docs.godotengine.org/en/stable/classes/class_separationrayshape3d.html

[ahintoflime]

I'd like to add that the documentation for the 3D separation ray page says this:

"A 3D ray shape, intended for use in physics. Usually used to provide a shape for a CollisionShape2D." which just doesn't make any sense at all

[MewPurPur]

I made the goof-up here, I'll edit it tonight.

[akien-mga]

Fixed by godotengine/godot#82544.