Notifies showing magnification switch when the touch interaction starts or ends

In the previous design, we notify syetem UI that magnification scale
is changed and it is time to show the magnification switch button.
While the new UX behavior is changed now, we want system UI get
the notification whenever a user touch interaction on the screen starts,
ends  or cancels when the magnification is activated.
Doc: go/window-magnify-ux ,page3

Bug: 172631612
Test: atest AccessibilityManagerServiceTest FullScreenMagnificationGestureHandlerTest
  MagnificationControllerTest WindowMagnificationGestureHandlerTest
Change-Id: Id3243702e8edea98da5c1230fd8d74973f002377