Fix ShowHelpHandler by running with RequiresForeground (#1970)

This was broken after the rewrite because we'd forgotten to specify that
it needs the foreground (which implies too that it must run
immediately). Now the script actually executes, either showing the help
in the Extension Terminal (or...I guess nowhere for clients without it)
or opening the URL it found. This should still be rewritten properly to
return the help over LSP and do something better with it, but at least
it's no longer broken.

src/PowerShellEditorServices/Services/PowerShell/Handlers/ShowHelpHandler.cs

@@ -67,7 +67,15 @@ public async Task<Unit> Handle(ShowHelpParams request, CancellationToken cancell
 
             // TODO: Rather than print the help in the console, we should send the string back
             //       to VSCode to display in a help pop-up (or similar)
-            await _executionService.ExecutePSCommandAsync<PSObject>(checkHelpPSCommand, cancellationToken, new PowerShellExecutionOptions { WriteOutputToHost = true, ThrowOnError = false }).ConfigureAwait(false);
+            await _executionService.ExecutePSCommandAsync<PSObject>(
+                checkHelpPSCommand,
+                cancellationToken,
+                new PowerShellExecutionOptions
+                {
+                    RequiresForeground = true,
+                    WriteOutputToHost = true,
+                    ThrowOnError = false
+                }).ConfigureAwait(false);
             return Unit.Value;
         }
     }