`Launch position` SUI controls not active unless X/Y values are entered first.

### Windows Terminal version

main 5608cf15

### Steps to reproduce

- open SUI and select `Startup`
- uncheck `Use system default` and try to change `Launch position` using up/down arrows

### Expected Behavior

- set terminal launch position using up/down arrows

### Actual Behavior

- controls not active unless a X/Y coordinate value is entered first:

https://user-images.githubusercontent.com/3933920/194438800-4c896d3b-4eac-40e1-bd38-8d2e6124375d.mp4

Upon unchecking `Use system default` launch coordinates should be set to '0' and up/down controls activate.

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ALTERNATIVELY:

> As the title describes, when the Launch Position is first shown, give the current position greyed out as the x and y position.
> When the Let Windows Decide is unchecked, un-grey out the x and y position and with each change of the x and y position, move the current window to match the new position. If I move the window on the screen manually, automatically update the x and y positions.

Reproduce the issue in Windows Terminal's SUI under Startup by unchecking Use system default and using the Launch position arrows. Inspect the Launch position controls and make sure unchecking the default initializes X/Y to 0 and enables the arrows; done means the position can be changed without entering coordinates first.

Written by the indexing model from the issue text.