Use TYPE_ACCESSIBILITY_MAGNIFICATION_OVERLAY for windowless window mag.

TalkBack currently is unable to swipe-to-move the focus off of
TYPE_ACCESSIBILITY_OVERLAY windows, including this mag window or any
other window of that type. See b/335440685.

It has no problems using TYPE_ACCESSIBILITY_MAGNIFICATION_OVERLAY (the
old type for this window, before windowless fix) so this change reverts
to that type until b/335440685 is resolved.

Fix: 327079186
Test: Use TalkBack to focus on the windowless window mag window. Then
      swipe left/right and observe focus is moved to another UI element.
Flag: ACONFIG com.android.systemui.create_windowless_window_magnifier TEAMFOOD
Change-Id: I7dcc1ad0e702fc1d8edcce333a9aab93deb51428