Single Executable WebEngine

WebEngine currently requires a helper process. This can cause some issues with sandboxing and deployment for some customers.

Chrome runs without a helper process, reusing the main executable as the helper process. We could enable the same way of running, though doing so would affect the command line interface of the hosting application and would thus need to be opt-in.

This is also necessary for network out-of-process, and static linking webengine features