664: Integrate ETC and ASTC textures in Skybox example r=kvark a=cwfitzgerald
Depends on https://github.com/gfx-rs/wgpu/pull/1074
Converts skybox example to mip-mapped files in:
- Bgra8
- Bc1
- ETC2
- ASTC4x4
Looks quite good now with mipmapping and trilinear filtering even at small resolutions.
Co-authored-by: Connor Fitzgerald <connorwadefitzgerald@gmail.com>