[BREAKING] Wrap ShaderSource::Naga in Cow<'static>

[daxpedda]

Checklist

• Run cargo clippy.
• Run RUSTFLAGS=--cfg=web_sys_unstable_apis cargo clippy --target wasm32-unknown-unknown if applicable.
• Add change to CHANGELOG.md. See simple instructions inside file.

Connections
Depends on gfx-rs/naga#2013.

Description
I'm currently pre-compiling shaders and storing them as const, but ShaderSource::Naga wants to own naga::Modules, as far as I understand, for good reasons, because it stores them, so not owning them would be problematic. Using Cow<'static, Module>, solves this, even if it looks strange.

Testing
None.

[grovesNL]

Could you provide an example that this change fixes? Is there another way to handle it without changing this type?

[daxpedda]

// I'm hiding some stuff here, but I've done this with a proc-macro
// and using `serde` to deserialize the `Module` in a `Lazy`.
const MODULE: &'static Module = ...;

// With the PR.
let source = ShaderModuleDescriptor {
    label: None,
    source: ShaderSource::Naga(Cow::Borrowed(MODULE)),
};
// Without the PR.
let source = ShaderModuleDescriptor {
    label: None,
    source: ShaderSource::Naga(MODULE.clone()),
};

// With the PR, I can now keep re-using the `Module` without having to clone it unnecessarily.
device.create_shader_module(source);

I hope this explains it.

On a side note, this change would also solve the lifetime issue in #2890. (it wouldn't, because it's 'static)

Is there another way to handle it without changing this type?

Not that I'm aware of, unless we want to carry around a lifetime I guess.

[daxpedda]

Probably related: #2801.

[daxpedda]

Now that gfx-rs/naga#2013 was merged, I updated the relevant parts to depend on it.

[daxpedda]

I think CI isn't failing because of this PR, it fails with the same errors in the latest commit on master too.

[cwfitzgerald]

I'm game, small comment

[daxpedda]

Added CHANGELOG entry and rebased, not sure why CI fails now, but it doesn't look like it's because of this PR.

[daxpedda]

Rebased after #3008.

[cwfitzgerald]

Hopefully this doesn't start another cowpocolypse 🐄 😆