Makes TYPE_ACCESSIBILITY_MAGNIFICATION_OVERLAY as trusted overlay

A MotionEvent dispatched within the area of trusted overlay
would not referred as an obscured event even a trusted overlay
overlaps other windows.
If a MotionEvent is referred as obscured when clicking accessibility
settings dialog, it would stop users from switching on an accessibility
settings and show a warning toast.
This change could make magnification window as trusted overlay that
users able to switch on an accessibility setting by touching inside
the area of the magnification window.

Bug: 144075853
Test: Verified an a11y settings is abled to be switched on when
the MotionEevent is dispatched within the magnification overlay.

Change-Id: I83a6ce1f6e66c55c45746e5a16d0d988d1c1ae0b