Improve detection of runspace changes

This change adds new behavior that makes the detection of sudden runspace
changes much more reliable.  These changes were particularly necessary for
detecting when we start debugging a runspace in a remote session since we
don't get a PushRunspace notifications when that happens.

This change also improves how we gather the prompt string just after a
command is executed.

Author: daviwil

src/PowerShellEditorServices.Protocol/Server/DebugAdapter.cs

@@ -742,7 +742,9 @@ await this.SendEvent(
 
         async void powerShellContext_RunspaceChanged(object sender, RunspaceChangedEventArgs e)
         {
-            if (this.waitingForAttach && e.ChangeAction == RunspaceChangeAction.Enter && e.NewRunspace.IsAttached)
+            if (this.waitingForAttach &&
+                e.ChangeAction == RunspaceChangeAction.Enter &&
+                e.NewRunspace.Context == RunspaceContext.DebuggedRunspace)
             {
                 // Send the InitializedEvent so that the debugger will continue
                 // sending configuration requests