Cleanup changes when cancelling the Add Game action

[arielj]

Problem description

If a user clicks Run Installer First in the Add Game dialog, it will create a prefix if needed and install the game/app. If the user then closes the dialog without finishing the process, the prefix is left there.

Feature description

We could keep track of what was done so far and suggest some actions if the user wants to close the dialog:

• if a new prefix was created, we can prompt the user to delete the prefix (we don't want to prompt to delete a shared prefix, only if it was just created)
• if an installer was executed in a prefix that already existed, we should let the user know that those changes will stay, that they may need to use something like winetricks to run the real uninstaller of that tool

I'm not sure if there's any other possible cleanup.

Alternatives

I don't know, current alternative is to know how things work and go and do things manually

Additional information

No response