backport #4695 [naga] Let constant evaluation handle Compose of Splat.

[Elabajaba]

Connections
Backports #4695 to the wgpu 0.18 branch (naga 0.14).

Description
Nested wgsl vec creation (eg. vec3<f32>(vec2<f32>(1.0), 0.0)) spits out vulkan validation errors. This backports the fix for it to naga 0.14 so that devs writing bevy shaders don't have to change shaders to avoid the validation error.

Testing
Examples still seem to run, and it fixed the vulkan validation errors when using eg. vec3<f32>(vec2<f32>(1.0), 0.0).

Checklist

• Run cargo fmt.
• Run cargo clippy. If applicable, add:
  • --target wasm32-unknown-unknown
  • --target wasm32-unknown-emscripten
• Run cargo xtask test to run tests.

cargo xtask validate spv kept failing with [ERROR xtask::result] 'spirv-val' failed to run; exit code: Some(1) despite spirv-val being in my PATH on windows.

• Add change to CHANGELOG.md. See simple instructions inside file.

Not sure how the changelog should look for the backport. Should I just copy the same message as in the changelog on trunk?

[Elabajaba]

Whoops, screwed up the cherrypick.

edit: #4833 for the fixed version with correct attribution.