Closes #2222e

Closes #2222

Currently, the semantics of RegistrationShutdown are confusing. Its only affect connections that are currently created and registered. This means connections in the process of being created, or connections created after registration shutdown are not taken into consideration. Additionally, this can cause a shutdown event before a connection is returned to a user, which makes using the API much more complicated then it should be.

This change does 3 things.
1. After it is called, it doesn't allow any more connections to be created on the registration.
2. Any connections opened but not started will not receive a conn shutdown event from the registration shutdown event until they are started. This way the user knows no events on the connection will be called unless they either start the conn or explicitly shut it down or close it themselves.
3. If an open connection is started after registration shutdown, it will immediately shut down with the error code given by registration shutdown.

Some tests are added as well to verify this behavior. More are needed, but this is a start.

__Originally posted by @thhous-msft in https://github.com/microsoft/msquic/pull/2226__