Properly import hdr/exr images from vpx tables

[rbxnk]

We need to find a way to import hdr/exr data into a Texture2D (or cubemap, if it turns out vpx only uses these for reflections). See TextureExtensions.FromHdrBinary. It's worth noting that the Unity editor itself can import these types of files just fine if you drop them into the project. But there does not appear to be an API for them which we'd need for the runtime import flows.