MagnificationPreferenceFragment use DashboardFragment

- Move preference related logic to Controller
- Add settings:controller in xml file

Bug: 73899467
Test: manual
Test: make RunSettingsRoboTests

Change-Id: I3eaccc617c4408f50110bf1f5df3482f491f7393
Signed-off-by: rafftsai <rafftsai@android.com>