Magnification pans diagonally with same radius as straight.

Also fixes bug where modifier keys lifted before arrow
or +/- keys didn't stop scaling or zooming.

Bug:388847283
Test: atest MagnificationControllerTest
Flag: com.android.server.accessibility.enable_magnification_keyboard_control

Change-Id: Ia8e28d12f152885263e05b349edccff1fb5fd282