This is a much simpler attempt to solve the same problem as #76060, but without breaking any compatibility.
* Adds a description of what model space is in the Vector3 enums (MODEL_* constants). This has the proper axes laid out for imported 3D assets.
* Adds the option to `look_at` using model_space, which uses Vector3.MODEL_FRONT as forward vector.
The attempt of this PR is to still break the assumption that there is a single direction of forward (which is not the case in Godot)
and make it easier to understand where 3D models are facing, as well as orienting them via look_at.
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