update switch UI if display magnification request is from external

Display magnifier could be magipulated by public API. This request
should be treated as an user interaction. We should also update the
magnification button in such circumstance.

Besides, we also disable display magnification that is requested
by AccessibilityService  when window magnification is enabled.

In the test part, we also verify the shorct trigged in full-screen
mode.

Bug: 179446412
Test: atest MagnificationControllerTest
      manually Test: Use voice access to controll display magnifier
      and chek if switch button is shown.
Change-Id: I729ea6fbf921ba6bd735c62198a2b8caee6ec4d7