This command is a helper command to be used by dlv dap when
launch request with a console property (integrated, external)
is received. The dlv dap server then asks the client to run
this command in the integrated or external terminal using the
RunInTerminal request and turns itself into a proxy mode that
forwards messages between the client and the dap-reverse command
run by the editor.

The dap-reverse command is similar to the dap command, except
that instead of opening a port and running as a server listening
on the port, this command dials to the supplied address (the
rendezvous port setup by the dlv dap server operating in proxy
mode). Once the dlv-reverse command is connected, the dlv dap
server will forward all the messages from the client (including
the initialize request and the launch request) and relay all
the responses from the dlv-reverse back to the client.

This command is internal use only, so it's intentionally hidden
from users - dlv usage and manual will not display info about
this.

Update golang/vscode-go#124

--connect=host:port flag will make dap subcommand launch the single session
DAP process in reverse mode.

Combined NewServer and NewReverseServer.

Restructure code to work with Session/Server.

This commit made misuse of Run and RunWithClient trigger fatal
logging which will print the call stack (so one can easily spot
how it was called) and terminate the process.