GLTFLoader: KHR_animation_pointer import support

add some TODO comments, rename pointer path property
wip support for camera and light properties, added morph target support
formatting, fix alphaTest, add opacity track splitting
added some comments, added some material ext animation properties
fixed Ior > IOR, test switching to node names to avoid duplication problems (but incomplete yet, needs full paths)
fix: use "pointer" property instead of "path"
refactor: move to extension, add new callbacks
move remaining pieces into extension, rename methods
fix: orthographic/perspective camera, pbrMetallicRoughness prefix, clearcoat/sheen/specular extensions
rm change on PATH_PROPERTIES
only patch PropertyBindings if KHR_animation_pointer is actually used
fix: fall back to original findNode implementation earlier if special cases don't yield results
introduce animationPointerResolver to allow configuring KHR_animation_pointer from outside
fix: glTF camera fov is in radians, not degrees
fix: use QuaternionKeyframeTrack instead of ColorKeyframeTrack if property ends with .quaternion
use extension hooks

Author: hybridherbst