Rethink modal dialog

[Tyriar]

Testing #226

When changing the shellStartup setting we see this:

I think the plan is to enable this by default so this isn't a good solution in the long run.

• Should this be a notification with apply/do not ask again? Is there a better presentation we don't yet support in the extension API?
• Should this only attempt to replace the terminal in question? You can get the shell via Terminal.creationOptions.shellPath ?? env.shell. I don't really want the python extension in VS Code to edit all my shell scripts or none of them.

[karthiknadig]

We don't plan on keeping this. I added this as a check so we can take backups before we do TPIs.

I agree that we should only modify shells that used by the user, and if the user runs or opens a new terminal of different type we can trigger and update that profile. That is a separate issue.