Add controller for magnification feedback preference

The controller's logic determines the visibility of this preference
based on the availability of surveys, as reported by
SurveyFeatureProvider.isSurveyAvailable.

Bug: 380346799
Test: atest MagnificationFeedbackPreferenceControllerTest
Flag: com.android.server.accessibility.enable_low_vision_hats
Change-Id: I7fe7aa4418a6be38e9e7af7efc76a9a25266198b