Better basis universal textures support

[beicause]

Bevy uses basis-universal-rs crate which is not actively maintained, lacks support for UASTC HDR, ASTC HDR, and the newish ASTC4x4-12x12, XUASTC4x4-12x12 in basis universal v2, and lacks web support.

Another problem for bevy is that basis universal textures can be standard ASTC, which means ktx2 loader can't distinguish them and can't transcode them when needed. One possible solution is splitting basisu loader from ktx2 loader and using .basisu.ktx2 extension to distinguish.

I made a crate https://github.com/beicause/bevy_basisu_loader that solved the problems.

I'm not sure if Bevy plans to improve basis universal support, or if it should be deprecated and left for community crate.