Make TestQuickly work again now that Debug commands are in an extension

Since the Debug commands have been moved into an extension, we can't directly call `_runTestSuite()`, and we can't actually add to the Debug menu since it might not have been created before we're loaded.

We really need the whole extension cross-dependency thing solved :), but until then, this just calls the command by string ID, and just adds the Cmd-P keybinding without trying to add it to a menu.