Fix a-asset-item binary glTF file loading

[Ely-S]

Description:
Fixes loading of binary glTF files by determining the file type using the glTF header. #4219

Changes proposed:

• When loading resources using a-asset-item, aframe determines the response type (text or arraybuffer) by checking to see if the requested resource has a .glb/.gltf file extension. This solution failed when loading resources with query parameters at the end (e.g /file.glb?version=1). This fix checks for the presence of the glTF magic number in the response body to determine if it should be treated as binary glTF data or text.

[dmarcos]

This breaks loading of the glTF file loading in examples: /showcase/shopping/ and /examples/showcase/anime-UI/

On console:

components:gltf-model:warn JSON.parse: unexpected character at line 1 column 1 of the JSON data