flutter/engine#19896 adds APIs for using an engine directly, allowing for headless execution, but there are still completely separate paths for creating and destroying an engine that's created directly vs. one that's created by the view. The C API should better reflect the internal structure, and the other platforms' APIs, such that there's cleaner integration between them. This also manifests in the C++ wrapper, where APIs are currently duplicated in the two classes instead of being managed through the engine wrapper (since creating an engine wrapper includes ownership of the engine).