Fix magnification border includes taskbar

The window type of the Taskbar is navigation_bar_paenel, which
is unmagnifiable. However, we used to exclude these windows from
magnification region computation to avoid cutout.

When the foldables is unfolded, the taskbar wouldn't cause the cutout.
To fix this problem, so we add a flag to distinguish the windows
that cause the cutout.

Bug: 196510717
Test: manual test
      atest AccessibilityManagerServiceTest
Change-Id: I882bf48585f646cee5827044c88da37250041c0f