Add HaTS entrypoint for Magnification page

This entry point allows users to access and adjust Magnification
settings for low vision accessibility. Visibility is controlled by
the aconfig flag and SurveyFeatureProvider#isSurveyAvailable.

NO_IFTTT=Revisit preference_list scope

Bug: 380346799
Test: atest ToggleScreenMagnificationPreferenceFragmentTest
Flag: com.android.server.accessibility.enable_low_vision_hats
Change-Id: I81a55487734fe7b139391a6c95834c7313e54d7a