Make include_spirv! actually work statically

[clarfonthey]

Description
Right now, include_spirv! cannot be used to directly define a static variable with the shader due to the wgpu::util::make_spirv_raw function not being const. This updates the macro to use an alternative implementation compatible with the current MSRV policy.

Note that the make_spirv_raw function is still not const because it accepts arbitrary input which may not be aligned, and thus allocates a new buffer for unaligned input. Instead, we use a separate function for the macros which can guarantee the alignment of the bytes being included.

Testing
Previously, this macro was not tested at all, and actually, include_spirv_raw had broken due to a change in the definition of ShaderModuleDescriptorPassthrough. Now, both include_spirv and include_spirv_raw are tested with a tiny "shader" file (it just contains the magic number + 0x11223344) to verify that the macros actually include a valid struct, and a proper test for the functionality is added to a wgpu-include-spirv test crate.

Squash or rebase? Squash.

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.

[clarfonthey]

Unfortunately, we lose the ability to output the magic number here, since formatting doesn't work in constants. While there are workarounds that work with the current MSRV like the const_panic crate, I decided that this isn't a massive loss and it was better to not add more dependencies.

[Wumpf]

Looking great, thanks for adding all those tests!
Albeit, see comment, to keep in line with the rest I think we should arrange this differently

[clarfonthey]

The latest commit removes the test binary and splits the tests across the macros and util modules. Hopefully this is good to merge, but if you have any additional feedback, let me know.

[Wumpf]

nice!