spirv: derive Hash and impl AsRef

[Firestar99]

glam spirv PRs 1/3:

• this PR
• spirv: vector attribute #676
• Revert: Don't use bytemuck derive on spirv. #677
• rust-gpu integration: abi: Make glam types abi layout match CPU Rust-GPU/rust-gpu#380

Objective

• remove unnecessary spirv feature gates
  • #[derive(Hash)]
  • impl AsRef for XXX

All of these features compile successfully on spirv, but may fail to link if they are used by shader code. They don't need to be feature gated explicitly by glam. Removing the feature gate now allows future iterations of the compiler to make the failing constructs work without having to first update glam to remove these feature gates.