Add support for Transform2D/3D in lerp()

[aXu-AP]

Implements godotengine/godot-proposals#10579

[Mickeon]

The supported types are listed in the description so that should be updated as well.

[fire]

@lyuma @TokageItLab Transform2D and Transform3D lerps are not really lerps anymore since it's a composite of lerp position, lerp scale and slerp rotation, but from a usability point of view I have nothing blocking it.

👍

[aXu-AP]

Transform2D and Transform3D lerps are not really lerps anymore since it's a composite

Well, lerp of Vector3 is also a composite of lerp of 3 floats and slerp is a different story altogether so I think transform interpolation goes well in to the mix...
If the user calls lerp(transform), there's no mistaking what the user intents to do.

I now changed the description as well. Also fixed a small factual error in the description (instead of clamping the output, weight should be clamped, since not all output types can be clamped).

[fire]

Your arguments to add Transform2d and Transforms3d makes sense for usability.

[akien-mga]

Makes sense to me.

[akien-mga]

Thanks!