Add Loader for GlTF SubAsset

[gz65555]

Is your feature request related to a problem? Please describe. I have a material only need a texture of glTF asset, but I don't want to parse all the glTF Asset.

Describe the solution you'd like Use q as query param. If the param is textures[0] which to get glTFResource.textures[0].

engine.resourceManager.load('.glTF?q=textures[0]');
engine.resourceManager.load('.glTF?q=materials[0]');
engine.resourceManager.load('.glTF?q=animations[0]');
engine.resourceManager.load('.glTF?q=meshes[0][0]');

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