Add support for glTF extension: KHR_texture_transform

[raytranuk]

Add support for glTF extension: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_transform

Currently failing related tests on: https://github.com/cx20/gltf-test:

Priority of this may change if users request / require this extension to be supported.

[slimbuck]

Note that we already support the scale and offset attributes of this extension https://github.com/playcanvas/engine/blob/master/src/resources/parser/glb-parser.js#L923.

[cx20]

@slimbuck

I tested it on the latest version of PlayCanvas and noticed that the results have changed.
Is this an expected change?

Library	TextureTransformTest.gltf result
PlayCanvas v1.44.2
PlayCanvas v1.45.0

[cx20]

I don't know if it's related to the above, but I can see some changes in the test results of the KHR_mesh_quantization extension model.

Library	Duck/glTF result	Duck/glTF-Quantized result
PlayCanvas v1.44.2
PlayCanvas v1.45.0

[slimbuck]

Thanks @cx20, I will address the texture transform issue.

[cx20]

Thank you so much.
I have confirmed that TextureTransformTest.gltf and glTF-Quantized Duck.gltf are displayed correctly in PlayCanvas v1.46.0.

[cx20]

I think TextureTransformMultiTest.gltf has also improved considerably.
There seems to be some issue about Unlit and Clearcoat Normal.

PlayCanvas v1.45.3	PlayCanvas v1.46.0

[cx20]

Hmm, It is the display result of PlayCanvas v1.46.0 + TextureTransformMultiTest.gltf above, but it seems that a shader error is appearing. Is it a matter of usage?

playcanvas-latest.js:15394 

Failed to compile fragment shader:
  :
ERROR: 0:61: 'vUv0' : undeclared identifier
ERROR: 0:61: '=' : dimension mismatch
ERROR: 0:61: '=' : cannot convert from 'const highp float' to 'highp 2-component vector of float'

Tested environment:
Windows 10 + GeForce RTX 2060 + Chrome 92