feat(onefingerpan): hide the one finger pan settings when window mode only

Like MagnificationAlwaysOn toggle behavior, when the magnification
capability is window-mode only we'll hide the OneFingerPan toggle too.

Also do a small refactoring in MagnificationOneFingerPanningPreferenceControllerTest

Bug: 333821725
Flag: ACONFIG com.android.server.accessibility.enable_magnification_one_finger_panning_gesture TEAMFOOD
Test: manually
      atest MagnificationOneFingerPanningPreferenceControllerTest
      atest ToggleScreenMagnificationPreferenceFragmentTest
Change-Id: I8684b5bae5cbfc5b75fc4c14d2e9173b17d0fb02