Option to prevent quickpicks from dismissing other quickpicks

From https://github.com/microsoft/vscode/issues/141514 The basic problem is that two processes are running in parallel, which may both require some input from the user. If a quickpick/input is shown while another one is visible, the second one will cause the first to be dismissed. This shows up in launch configs, there is probably a task scenario that would show the same issue, or you could imagine other extension-based workflows that end up interrupting each other. For launch configs, we will add a queue to work around this, but when I am queueing two unrelated pieces of code just because they might trigger quick inputs way downstream, then it seems like I am solving the problem at the wrong layer. I'm not blocked by this issue, I just feel like it might come up again at some point. However, changing this for all quickpicks at this point seems odd and could possibly be a breaking change for some extension that relies on the dismissing behavior, even on accident.