Add glTF morph animation support (PoC)

[appgurueu]

This implements support for glTF morph animations.

This gives you an alternative way to animate vertices and normals (technically you could achieve this by having one joint per vertex, but for all but the most low-poly models that would be absurd).

Perhaps more interestingly, this lets you animate texture coordinates. (To give one example, this could be used to define a smooth clientside tile animation inside model files.)

It could also be applied to colors (which could enable cool effects, think rainbow or fake shine), but (1) we currently abuse colors for lighting and (2) our unsigned color format is currently unsuitable for storing the color deltas gltf demands.

Demo:

Screencast.from.2025-04-29.02-43-32.mp4

To do

This PR is a Work in Progress. Some TODOs are in-source / in commit messages.

How to test

Throw models using morph animations at it.

[kromka-chleba]

Perhaps more interestingly, this lets you animate texture coordinates. (To give one example, this could be used to define a smooth clientside tile animation inside model files.)

This would be especially useful for animating facial textures. Will this need SSCSMs given the "clientside" nature you mention or will there be server-side API to control this too?

[appgurueu]

This would be especially useful for animating facial textures. Will this need SSCSMs given the "clientside" nature you mention or will there be server-side API to control this too?

Right now it's just a model feature, these are just normal animations you'd set with ObjRef:set_animation.