This removes two Executor::Run dependencies, and requires that all ServerCallbackCall implementations implement the new `RunAsync` method. There's one other known other implementation of ServerCallbackCall that will need to be updated.
We could also support an "inefficient" path that uses the default engine (not implemented here), for all subclasses that do not want to update. As far as anyone is aware, the ServerCallbackCall class was never intended to be subclassed externally.
Closes#36126
COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36126 from drfloob:server-callback-on-ee 6242a78a3f
PiperOrigin-RevId: 619621598
3d82c522fa