OpenEXR export

[rawnsley]

Added support for OpenEXR by defining a new extension MOZ_texture_exr

Here's an example Blender scene with EXR images for testing: https://github.com/LearnHub/HubHenge/tree/exr-version

[rawnsley]

@keianhzo coincidentally this PR addresses this comment you added last year

[Exairnous]

The code seems good. This isn't a user facing change, so I don't see any problem with adding it, but I thought that supporting EXR wasn't a direction the Hubs team wanted to go in right now, so has that changed, or is this something you need for your client? I think EXR support is nice to have, so thanks 🙂 I'm a bit curious though.

[rawnsley]

I discussed our use case in this companion PR, but basically EXR format is a better intermediate format to go into our post-processing tools as it preserves precision and has a wide range of layout options including alpha channels and file compression. We added support in Hubs itself because it is sometimes useful to review the scene without post-processing and compare before and after.

[Exairnous]

Ah, okay. Thank you.