wiggle: delete GuestErrorConversion, improve some error reporting

[pchickey]

With the latest renovation to witx, wiggle no longer generates code that calls the GuestErrorConversion trait to transform a GuestError into the function's error type. Instead, wiggle will trap execution if a GuestError is thrown in generated code.

This PR removes generation of the GuestErrorConversion trait. Users can delete their impls of it - they are dead code.

I also fixed up the Display impl of the GuestError::InFunc variant to be more useful, and deleted GuestError::InDataField because it was also dead code.

[github-actions]

Subscribe to Label Action

cc @kubkon

Details

This issue or pull request has been labeled: "wasi"

Thus the following users have been cc'd because of the following labels:

• kubkon: wasi

To subscribe or unsubscribe from this label, edit the .github/subscribe-to-label.json configuration file.

Learn more.