Enable use_collision on CSGShape3D by default

[Calinou]

Related to #59266 (can be merged independently).

Since collision is often desired for level prototyping (and most CSG nodes are intended to be solid), it makes sense to enable collision by default.

See discussion in godotengine/godot-proposals#2879 for further rationale.

[stebulba]

When you use CSGPolygon to fallow a path in Editor, during prototyping you don't need the collision until you are satisfied with the result. That will just overload the physic server for noting by default.
I am not sure with this PR.

[Calinou]

When you use CSGPolygon to fallow a path in Editor, during prototyping you don't need the collision until you are satisfied with the result. That will just overload the physic server for noting by default. I am not sure with this PR.

We could make collision be generated only when running the project by default (using Engine::get_singleton()->is_editor_hint()). If you need CSG collision within the editor (e.g. for use by an editor plugin), we could have a project setting to enable this.