[vm] Move native assets yaml to embedder instead of VM

[dcharkes]

Tracking issue for the Dart-side of the work proposed in flutter/flutter#154425 by @mkustermann:

• Move the native assets mapping understanding from the VM to the standalone embedder (https://dart-review.googlesource.com/c/sdk/+/379781 and [vm][cfe][frontend_server] Make "native_assets.yaml" reusable #55826).
• Change the embedder API to work on asset ID instead of asset path.

To ease the roll into Flutter, this will likely need to be done by introducing the new API first and then removing the old API in NativeAssetsApi.

[dcharkes]

This can be done after v1.0