Convert Magnify controller to TogglePrefController

Convert below to TogglePreferenceController:
MagnificationNavbarPreferenceController
(Magnify with Button)
MagnificationGesturesPreferenceController
(Magnify with triple-tap)

The two controllers share the same fragment,
Add static method for set/get state in fragment,
And use them in controllers and fragment.

Change-Id: I2bdbdb36be71e1a3ffb557abc5a6115d48de53cf
Merged-In: I2bdbdb36be71e1a3ffb557abc5a6115d48de53cf
Fixes: 67997698
Fixes: 67997726
Test: make RunSettingsRoboTests