feat(EDT): Update the force dark theme trigger condition

The original method of observing UiModeManager#ForceInvertChangeListener
led to memory leaks due to frequent activity changes. Switching to a
settings key observer provides a more stable and leak-free solution.

Bug: 368721320
Flag: android.view.accessibility.force_invert_color
Test: atest ViewRootImplTest
Change-Id: I99ea786e393c0945c3a1aee41a1e8240f94223e3