This cleans up the magnification mode controller and related code. It
also fixes most of the lint errors in the files.
NO_IFTTT=linter not working
Bug: b/388335935
Flag: EXEMPT refactor
Test: com.android.settings.accessibility.ToggleScreenMagnificationPreferenceFragmentTest & com.android.settings.accessibility.MagnificationModePreferenceControllerTest
Change-Id: I368128c3c71285a9511a7831e1d01232e7536d2f