Fix magnification cutout while performing back gesture

The window type of edge panel is nagivation bar panel,
which is not magniiable so wouldn't be included in the
magnification region. To fix it, we exculde this window
while computing magnification region

Bug: 208720902
Test: manual test
Change-Id: I2209cc307f2177c55175b35b71b28d6b4e28a05b