• Update code that uses .isCompatibilityMode to also understand .featureLevel.
  • As mentioned in Update print_environment to show featureLevel and defaultDevice #4130 and Compat: remove GPUAdapter.featureLevel gpuweb#5037,
    we'll need to figure out how getDefaultLimitsForAdapter() could work if we don't have either of these.
• Update the test to understand .isCompatibilityMode, .featureLevel, or .features.has('webgpu-core')
• Update all comments about removing compatibilityMode: boolean.

We could probably remove compatibilityMode already? But I'm not sure. We can do that in a separate step.

Issue: None

Requirements for PR author:

• All missing test coverage is tracked with "TODO" or .unimplemented().
• New helpers are /** documented */ and new helper files are found in helper_index.txt.
• Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)
• Test have be tested with compatibility mode validation enabled and behave as expected. (If not passing, explain above.)

Requirements for reviewer sign-off:

• Tests are properly located in the test tree.
• Test descriptions allow a reader to "read only the test plans and evaluate coverage completeness", and accurately reflect the test code.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Helpers and types promote readability and maintainability.

When landing this PR, be sure to make any necessary issue status updates.