Move magnification-relatd stuff to MagnificationController

We moved most of magnification-related stuff to MagnificationController
to centeralize the common magnification logic and the interaction
between magnification modes.

Test: atest CtsAccessibilityServiceTestCases
      atest com.android.server.accessibility
      atest com.android.server.accessibility.magnification
Change-Id: I30face9d94a29844dfa1d4a98139628bf1d79fec