Use case

Custom entry point for flutter engine is useful, relate to #86599 .

Although there is already relevant implementation method on windows. FlutterWindowsEngine::RunWithEntrypoint. But this method always passes in a null value here, and it cannot be modified in the flutter app/plugin project.

Proposal

Add a new property custom_entry_point to flutter::DartProject, and run FlutterWindowsEngine with custom_entry_point.