Design a way for TerminalConnections to receive arbitrary (JSON?) arguments

[DHowett-MSFT]

This will allow a connection type to peer into the profile that spawned it to get more information out of it, like a port from a telnet profile and a username from an SSH profile.

[zadjii-msft]

More or less, this was done with #10184. A ValueSet is basically a jsonblob. Whenever we eventually get around to allowing other connection types, that's how we'll do it.