Logs magnification feature behavior. (2/2).

Uses the atom MagnificationModeWithImeOnReported in westworld to log
the activated mode when the IME window is shown on the screen.

Adding a new callback API in the MagnificationCallback to monitor the
IME window visibility changes. The A11y framework registers the
callback when the magnification is enabled. It logs the related
data when it receives the IME window visibility changes through
this callback and the magnification is in the activation.

Bug: 154021596
Test: a11y CTS & unit tests
Test: make statsd_testdrive && ./out/host/linux-x86/bin/statsd_testdrive 346
Change-Id: I49b02e00d5a1131b388eeb923440f59a2b4f81a6