[WIP] Update spirt to 0.5.0.

[eddyb]

Will stay as draft until spirt 0.5.0 is released, containing at least:

• Rename ControlRegion to just Region. spirt#7
• Rename ControlNode to just Node. spirt#8
• Replace Attr::SpvDebugLine with a better basic debug source location attribute. spirt#9
• "Unintern" DataInstForm (inlining its fields back into DataInstDef). spirt#12
• Update SPIRV-Headers to match Vulkan SDK 1.4.363.0. spirt#49
  • this gets ahead of rspirv (see Regenerate on vulkan-sdk-1.4.363.0 gfx-rs/rspirv#280),
    so that spirt will (hopefully) not block the use of newer extensions
• Minimal support for several SPIR-V features (either new, or rare edge cases, some Rust-GPU specific). spirt#52
  • this is the main motivation for doing this sooner than later (see below)
• spv: minimal OpSpecConstantOp and OpConstantFunctionPointerINTEL support.  spirt#22
• spv/lift: elide empty targets of an if-else/switch, as allowed by SPIR-V. spirt#28

---

This came about because of OpExecutionModeId/FPFastMathDefault, wanted by:

• Adhere to Rust floating-point semantics #643
  (cc @jlogan03, you might be able to test by rebasing on top of this branch)

FPFastMathDefault takes:

• a type ID operand
  • this is itself unusual (as in, types as operands is rare), I've handled it via a Type-in-Const embedding that other extensions also ended up needing independently (e.g. OpUntypedPtrAccessChainKHR)
• a constant integer ID operand
  • not a literal (for specialization constants, maybe? the spec does mix IDs and literals elsewhere)

And any IDs being involved meant spirt::Attr::SpvAnnotation has to grow an extra field (which is even worse than just some Consts, because of how AttrSet relies on Attr: Ord etc.).

Hopefully the solution will cover anything else Rust-GPU may need for the next little while.

[jlogan03]

  (cc @jlogan03, you might be able to test by rebasing on top of this branch)

Thanks! I rebased on top of this branch and it works 🎉