KHR_animation_pointer support

[Igor-dvr]

"The base glTF 2.0 specification supports animating only node transformation or morph target weights. With this extension, an animation can target any mutable property in a glTF asset, such as material factors or camera field of view."

https://github.com/KhronosGroup/glTF/blob/main/extensions/2.0/Khronos/KHR_animation_pointer/README.md

Godot implementation godotengine/godot#94165