Fix the layout flag for magnification settings

Adding the flag FLAG_NOT_FOCUSABLE to enable interaction with the
screen below the layer of settings panel. The logic of requesting focus
on the settings panel when it is opened is also removed since
requestFocus does not work on the view with the flag.

Bug: 241996711
Test: manually - attach videos to the bug
Test: atest WindowMagnificationSettingsTest
Change-Id: Ib0aac29a27de14b1fa35b87fa840dd56ae00be6b