MagnificationProcessor uses MagnificationConfig to control the specified magnifier

MagnificationConfig stores the magnification configuration of the
controlling magnifier, such as magnification mode, scale and center
postion.
And MagnificationProcessor uses the config to controll the magnifier for
AccessibilityService.

See
API review doc: go/b200769372
Design doc: go/a11yservice_control_magnification_in_t
   The chapter at Proposal A and  MagnificationConfig
CTS: ag/15824302

Bug: 199732498
Test: atest AbstractAccessibilityServiceConnectionTest,
      atest MagnificationProcessorTest,
      atest WindowMagnificationManagerTest,
      atest MagnificationConfigTest
Change-Id: I20323865d2efe1b40626f0c86767848733856482