Changed enumerate_adapters to be able to work with custom backends

[R-Cramer4]

Description
When using a custom wgpu backend, you can't enumerate through the adapters to check compatibility because it checks if it is a Core Adapter. This change moves that code to the inner part of an Adapter so it can be a part of the AdapterInterface trait. This allows more functionality with custom backends.

Testing
Running all current tests

Squash
Commits will be squashed on merge

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.

[sagudev]

As I already said in on matrix, I think it would be good to export enumerate_adapters everywhere and make it return just one adapter on the web. But to make this work, we would need to make enumarate_adapters async.

[Wumpf]

I think biting the bullet and making enumerate_adapters async is the right call, not just because of the custom backend problem at hand but more so because it allows us to provide this also on WebGPU, elminating one of the weirder native/non-native distinctions. 👍

cc: @cwfitzgerald because this has been around for a long time and there might be repercussions I'm not thinking about right now

This being a breaking change that affects almost everyone, this should be mentioned prominently in the changelog.

[cwfitzgerald]

Discussed at the wgpu maintainers meeting. Resolution: Lets make this async and compatible with the web.

Discussion

• CF: I have some concerns about async
• AR: There’s already async in initialization, so this is not worse.
• CF: We can talk about improvements to the apis in general with async.
• TT: Doesn’t work on WebGL
  • Hasn’t changed from previous behavior but should make sure this is documented