[naga hlsl-out, glsl-out] Support atomicCompareExchangeWeak

[cryvosh]

Connections
Fixes #7578, related to #4364.

Description
Adds support for atomicCompareExchangeWeak translation to hlsl and glsl.

Note this does not implement the [allow_uav_condition] loop attribute mentioned here and here.
Not sure the best way to check if the loop termination is based off a UAV read.
Maybe can later borrow logic from the uniformity analyzer?
Dawn doesn't seem to do this either, though maybe it should?
There is a test with a while loop that depends on .exchanged which seems to pass hlsl validation.

Testing
Added / enabled some basic atomicCompareExchangeWeak tests to Naga.
My personal project using atomicCompareExchangeWeak runs fine now on Windows/Nvidia/DX12.
GL backend is untested outside the Naga tests / validation.

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.