update rspirv 0.11 to 0.12

[Firestar99]

The rspirv update is required to get the spirv symbols required for mesh shaders, which will be added in a separate PR. Original mesh shader PR: https://github.com/EmbarkStudios/rust-gpu/pull/1019

[Firestar99]

While porting, I've noticed that rustc_codegen_spirv::spirv_type_constraints::instruction_signatures(Op) somehow seems to validate a lot of SPIR-V Ops on their input and output types, and that spirv/grammar/autogen_table.rs seems to also contain a giant List of auto-generated instructions with all their inputs and outputs. Maybe something could be simplified there?

[Firestar99]

Basically ready to merge, apart from LiteralFloat still being a todo!. If it's essentially unused, should it just be replaced with some kind of error message, and done with it?

[eddyb]

This is really weird, looks like #1127 has caused GitHub to expect those CI changes here too:

~~But that PR hasn't landed, and it looks to pass all checks perfectly fine. Maybe GitHub incoherently caches some of this, leading to changes bleeding over between PRs?~~

~~Will try restarting CI for this PR to see if it fixes itself.~~

EDIT: oops, turns out @Jake-Shadle actually made repo-wide changes to the expected CI jobs, I just had no idea who has access to those settings (I don't atm, otherwise it would've been easy to check).

[eddyb]

@Firestar99 #1127 just landed, you'll need to rebase (but I should be able to review concurrently).