Fix to have only one PI instance at any point in time

[zadesai]

Summary of the pull request

If PI is running elevated, and a user starts PI unelevated, we would have 2 instances of PI running.
To fix this, when an elevated PI instance is running, redirect all activation calls to the elevated PI instance.

Validation steps performed

1. Run PI unelevated
2. Change target app to task manager
3. This shows a button to run PI as admin
4. Click on the button and wait for PI to run as admin
5. From unelevated powershell run PI and confirmed that the activation is redirected to the elevated PI instance.