Fix mod search textbox having focus while settings are visible

[peppy]

Stopped arrow key adjust on slider bars from working.

Also just felt wrong that you could type into an off-screen textbox.

Closes #25842

[bdach]

The way this is implemented is pretty hacky and directly fails one of the tests (TestSceneModSelectOverlay.TestSearchFocusChangeViaClick).

• If the search textbox starts focused, or gains focus via a Tab key press, it cannot be unfocused by mouse.
• If the search textbox does not start focused and is focused via mouse instead, it can be unfocused by mouse.

2023-12-18.20-38-48.mp4

I'm not sure what to make of that. Honestly seems like weird behaviour.

[peppy]

Hmm, I guess? Depends on how you see it working (HoldFocus makes it behave like the song select one while in focus mode).

Alternative would be making a tracking bool and handling focus more manually as per before. Should only require a few lines of change.

[bdach]

I'd also accept having both mouse and keyboard hold focus and not give it back (plus removing that failing test; rest should start passing with that change I believe). So long as you can't drop the focus one way but not the other.

[bdach]

#25880 also needs investigation here (potentially a regression from this PR as it was cherrypicked into the hotfix release)

[peppy]

I've reverted to a safer approach to handling this, let me know what you think. Not 100% sure on the private method taking an argument, can refactor that if required.

[bdach]

Seems okay. Have added appropriate test coverage.