Add compile_spirv proc macro to replace build.rs

[Hentropy]

Adds a proc macro that builds and executes a SpirvBuilder at compile time. This replaces the build.rs use-case of SpirvBuilder, but does not replace using SpirvBuilder directly if runtime shader compilation is desired. The macro returns the result of SpirvBuilder::build(), ie. the path to the .spv file.

Syntax:

compile_spirv! {
    // required
    path: "path/to/crate",
    // optional, defaults to 1.3
    version: 1.5,
    // optional, defaults to Vulkan
    memory_model: GLSL450,
    // either...
    debug,
    // ...or, default is release
    release,
}

[Hentropy]

This will unblock #423

[lachlansneff]

Does this work with emitting a spirv file for each entry point?

[Hentropy]

No, though it could be extended to do so. Another useful extension would be to have it return the spirv directly, instead of a path to a .spv file.

[XAMPPRocky]

Thank you for your PR! Can you update this to have the same options as the current build.rs version? E.g. Remove the version and memory_model arguments, and add the target and multi_module arguments?

Also I think the parsing logic for the arguments is a bit too overly complex in terms of the amount of duplicated code, I would use some macros to clean up the validation logic. You can see similar logic in my image macro PR.

[khyperia]

We should discuss this in the next meeting, this is a pretty major change with large tradeoffs and should go through at least the MCP process (or even an RFC, tbh) before being approved. Doing a request changes to make sure it's blocked before that happens.

[Hentropy]

Closing, unclear how #423 will end up working/if it will.