Establish new channel connection model using server listeners

[daviwil]

This change refactors our existing channel model to move all connection
logic outside of the ChannelBase implementations so that the
language and debug client/service pairs can be simplified. This change
also allows us to remove a long-standing hack in our Host unit tests
which added an artifical delay to give the channel and MessageDispatcher
time to get established.

[daviwil]

The basic idea here is that connections should be established before creating an instance of a ChannelBase implementation. This simplifies client and server implementation since they don't have to deal with waiting for a connection before proceeding. The assumption is that the ChannelBase implementation is connected and fully established before being passed to a ProtocolEndpoint implementation (like LanguageServiceClient, etc).

/cc @mrward @kamilkosek since it affects the LanguageServiceClient class and how you establish a TcpSocketClientChannel. Check out this code for example on how to set up a LanguageServiceClient with the altered model:

https://github.com/daviwil/PowerShellEditorServices/blob/90afbeb689c7ddb8be360de8bbf14c7fd694725d/test/PowerShellEditorServices.Test.Host/LanguageServerTests.cs#L53

[daviwil]

Not in a rush to merge this, I'll leave it open until later tomorrow in case anyone has questions or feedback!