* The embedder depends on dynamic:embedder
* The dylib depends on dynamic:dylib
* The embedder calls OnLoad and OnUnload callbacks that setup and teardown the dylib environment
* The dylib contains a thin library that services OnLoad, OnUnload and OnInvoke so that vendors dont have to do it themselves (and potentially mess it up)
* The vendor only has to implement the `FlutterServicePerform` method that takes a fully scoped handle
* This patch is a WIP till we get a stable Flutter ABI. The stuff in mojo/public is *NOT* stable
