Update default values for capability and mode

Update the magnification default capability to full screen to ensure
that we could always get the same capability as in accessibility service
for magnification.
Update the magnification default mode to window or full screen based on
current capability.

Bug: 284233505
Test: atest WindowMagnificationSettingsTest
Test: manually - check the settings panel falls into the case of full screen mode after performing factory reset
Change-Id: Iefd1eb4954bf823371b558fa7660a3c2cc9ed3d1