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

[elsaco]

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.

[lhecker]

An idea: We should maybe just move away from NumberBoxes and use regular input fields instead. This would have the benefit of simplifying the control (no buttons) given that most people most likely will enter text via keyboard.

[zadjii-msft]

We should dedup this with #17210 tbh