Singleton on any application

### Description of the new feature / enhancement

I have a calculator shortcut on my keyboard. Every time new instance is run of calc.exe. It would be nice to have option in PowerToys to select applications which should be run only in one instance. When I want to open new instance of calc.exe, the currently loaded application should be focused.

### Scenario when this would be used?

Calculator, notepad and other applications which should be run only as one instance.

### Supporting information

_No response_

No file, test, or entry point is named in the issue. Start by locating PowerToys' application-launch handling and determine how a selected executable could be configured, detected as already running, and focused; done means the option works for calculator, Notepad, and other selected applications without opening a second instance.

Written by the indexing model from the issue text.