spirv: impl Debug + Display, fix Affine::from_cols_array()

[Firestar99]

I would like to get a 👍 from the rust-gpu maintainers before this is merged, but feel free to already review this. Thanks :D

Added features for the spirv target:

• rust-gpu v0.9.0 added support for Debug and Display traits, this PR removes all the #[cfg(not(target_arch = "spirv"))] hiding the traits impls for the spirv target.
• Make Affine::from_cols_array() not use any slices internally and use arrays instead, as this caused compilation errors when these methods were used on the spirv target.

I tested this PR against embark's rust-gpu master branch and the latest v0.9.0 release using their compiletest suite.
(Note: test member_ref_arg-broken may fail on v0.9.0 due to a diff in stdout caused by newer spirv tools)

[eddyb]

rust-gpu v0.9.0 added support for Debug and Display traits

To be clear, running the derived impls isn't really supported, there's just some minimal panic! format string conversion to debugPrintf, mainly for simple scalars but I guess vectors are also supported?
(i.e. the only reason to have these fmt::{Debug,Display} impls is so that e.g. panic!("{some_vec4}") type-checks, before it can get transformed into the equivalent debugPrintf)

[Firestar99]

@bitshifter could we get this merged? Thanks :D

[bitshifter]

Sorry for the delay, GitHub didn't notify me that the PR had moved out of draft.