Expose ShapeCast{2D,3D}::get_collision_result

[raulsntos]

This allows language bindings like godot-cpp to access the read-only property collision_result. Although it's possible this property was meant to be internal. If so, we can just add the PROPERTY_USAGE_INTERNAL flag to the property instead.

• Contributes to Ignoring class methods with underscore prefix cause issue with some properties #64429.

[rburing]

Since the (read-only) property was already exposed, the getter should be too.

In fact the read-only property could be removed in favor of the getter, but in any case this is a good uncontroversial first step.

[akien-mga]

Thanks!