chore(#Magnification): add new field in metric MagnificationUsageReported

We add new field scale in metric MagnificationUsageReported. In
FullScreenMagnificationController/WindowMagnificationManager, we add
getLastActivatedScale method so that MagnificationController can get the
last magnification scale of the activation for logging.

Bug: 281287915
Test: atest MagnificationControllerTest
      m statsd_testdrive & statsd_testdrive 345
Change-Id: If45b43ae58ed05fb68575fc6bf15c551fc2026a8