Bb tex warn

Initial issue : #5337


fix/improve compressed texture availability check

- convert `_compressedTextureFormats` to real Array
- check if `glFormat` is found in  `_compressedTextureFormats` 

note : the check can't prevent gl warnings during draw call (texture is invalid)

```
Attempt to load unsupported compressed texture format 
...
...
[.WebGLRenderingContext]RENDER WARNING: texture bound to texture unit 0 is not renderable. It maybe non-power-of-2 and have incompatible texture filtering or is not 'texture complete' webgl_materials_texture_pvrtc.html:1
WebGL: too many errors, no more errors will be reported to the console for this context. 
```