Debug Console should give user warning message when executing command

[daviwil]

Now that we have the Integrated Console, the Debug Console should give the user a warning if they try to use it so that it's obvious that its use is deprecated.

[rkeithhill]

I wonder if this is worth submitting back to VSCode i.e. provide an option for a debug extension to disable the Debug Console? This would be for debug extensions that provide a REPL/debug terminal.