Refactor the `#[wasmtime_test]` macro

[alexcrichton]

• Start tests with a blank slate of features instead of with the default set of features enables (ensures each test explicitly specifies required features)

• Reuse test features from wasmtime_wast_util to avoid duplicating listings of features. Also shares logic for "should this compiler fail this test because of unsupported features".

• Move logic in tests/wast.rs to apply test configuration to a Config to a new location that can be shared across suites.

• Add a new feature for simd and flag tests that need it with the feature.

This is done in preparation for adding a new compiler strategy of Pulley to be able to flag tests as passing for pulley or not.

[github-actions[bot]]

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