[Magnifier-46] Add builder for magnifier objects

The CL adds a builder class that enables creating Magnifier objects with
custom properties. The defaults of the builder remain the predefined
values of the magnifier in P.

Bug: 72211470
Test: manual testing
Test: atest CtsWidgetTestCases:android.widget.cts.MagnifierTest
Change-Id: I066082fb17cfb8c483c49b7011abfa9dca9de77a