Support click metrics logs in several pages

- Assign metrics category to perferences at an earlier stage in
  DashboardFragment for better usability.

Bug: 137559984
Test: robotest
Change-Id: Icd4185efa0e655be20c4b673a1380fa42140923f

src/com/android/settings/accessibility/MagnificationEnablePreferenceController.java

@@ -20,9 +20,6 @@ import android.content.Context;
 import android.os.UserHandle;
 import android.provider.Settings;
 
-import androidx.preference.Preference;
-import androidx.preference.SwitchPreference;
-
 import com.android.settings.core.TogglePreferenceController;
 
 /** Controller that shows the magnification enable mode summary. */