Update window magnifier UI when onConfigurationChanged. (1/n)

This change would update UI when the display size is changed.
In the later changes, we will handle the case for device orientation
changed or a physical display is updated. And we have to keep
the mafnification area unchanged when the UI is updated.

Bug: 144664540
Test: manual test
Change-Id: I7cfac77e1d74c709013c9ed07600051ee9a34097