Accessibility shortcut secondary action - correct magnification shortcut logic

- correct magnification shortcut logic
- add magnification tests

Bug: 142530063
Test: make RunSettingsRoboTests -j52 ROBOTEST_FILTER=ToggleScreenMagnificationPreferenceFragmentTest
Change-Id: I15f8bccde63570e93e28399bc1730fb1afdb1242
2 files changed