Add warning when using CompareFunction::*Equal without an invariant Attribute

[cwfitzgerald]

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.

Description

This is a common issue that only actually manifests on specific sets of hardware (apple based gpus) and I know of no cases where this will be a false positive, so having a global warning for this is useful.

Testing

Tested by changing an example to use Equal.

[nical]

Nice! would it make sense for the warning to be only emitted in debug builds?
Edit: I guess it's up to the application developer to not output warning in release builds and the subject of this warning looks like it is not likely to be a false positive.

[cwfitzgerald]

Yeah I'm generally unconvinced that wgpu itself should be making any decisions (besides literal debug assertions) based off of debug_assertions - we should let the user decide what is best for them. In this case logging frameworks let you filter based on module as you please, so we should be okay here.