feat: const feature defaults

[MultisampledNight]

Connections
Link to the issues addressed by this PR, or dependent PRs in other repositories

Discussed on Matrix: https://matrix.to/#/!XFRnMvAfptAHthwBCx:matrix.org/$Nb3Nk7fnyG08QfzPnbxCvgBWnaPaYGRXqbC2ayHziCQ?via=matrix.org&via=mozilla.org&via=gitter.im

Description
Describe what problem this is solving, and how it's solved.

Previously, it was not possible to use the downlevel defaults in const as they were not marked as such. But nothing was stopping them from being marked const, as they are just sets of values.

Testing
Explain how this change is tested.

Not at all.

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.
  • 2 failed, specifically these, but the failures look unrelated to my changes and more like due my setup
    • wgpu_test::shader::struct_layout::uniform_input
[2024-03-05T09:33:43Z ERROR wgpu_test::expectations] Expected to fail due to [FailureReason { kind: Some(ValidationError), message: Some("a matrix with stride 8 not satisfying alignment to 16") }], but did not fail
    • wgpu-examples water
      test panicked: explicit panic although the comparison passed
• Add change to CHANGELOG.md. See simple instructions inside file.

[Wumpf]

neat, thank you!