Anonymous servers aren't registered statically, meaning they can't be referenced by name.
Only the InProcessSocketAddress, fetched via Server.getListenSockets()
can be used to connect to the server.

This is particularly useful for production Android usage of in-process servers,
where process startup latency is crucial, since a custom name resolver can be
used to create the server instance on demand without directly impacting
the startup latency of in-process gRPC clients.

This approach supports a more-standard approach to "OnDeviceServer" referenced in gRFC L73.
https://github.com/grpc/proposal/blob/master/L73-java-binderchannel.md#ondeviceserver

Tests require it.

Created a new AnonymousInProcessSocketAddress class which is
distinct from the existing InProcessSocketAddress.

This simplifies the server builder API since we can have
forAddress() instead of anonymous(), and removes the need for
InProcessSocketAddress to handle anonymous servers, which had some
tricy implications like getName() returning null.