Regenerate with final KHR Ray Tracing spec

[MarijnS95]

Depends on #173

The ray tracing specification is final 🎉 ! See https://www.khronos.org/blog/vulkan-ray-tracing-final-specification-release for more details.

We should hold off merging and releasing this until SPIRV-Headers drops the next tag so that we can version the spirv_headers crate properly.

[MarijnS95]

Turned TerminateRayKHR/IgnoreIntersectionKHR into terminals (see microsoft/DirectXShaderCompiler#3285, microsoft/DirectXShaderCompiler#3295, KhronosGroup/SPIRV-Tools#4050). Note that rspirv doesn't yet make the distinction between block terminals and execution terminators (these instructions + Kill + TerminateInvocation), is that something worth looking into? EDIT: Not interesting, these instructions still terminate a block and I don't see any special handling for returns and aborts either.

Also removed the Terminator class. In particular because it's not possible to write Some(Terminator) | (Some(Reserved) if ...) in a match block, but this class has never existed in the history of SPIRV-Headers. Bit misleading to keep it in until it actually shows up, right?

Finally, the version: Looks like we have 1.5.4, 1.5.4.raytracing and 1.5.4.raytracing.fixed... We can't represent that in semver and I have no idea if another proper version number bump is going to happen to land the RT spec (here's hoping these are "prerelease" indicators...).