[Magnifier-23] Fix invisible cursor in magnifier

Previously, if the magnifier was triggered when the cursor was invisible
between blinks, the cursor would remain invisible until its position
first changed as a result of user dragging. This CL fixes this, by
forcing the cursor to become visible when the magnifier is triggered.

Test: manual testing
Test: atest CtsWidgetTestCases:android.widget.cts.TextViewTest
Test: atest FrameworksCoreTests:android.widget.TextViewActivityTest
Bug: 72314929
Bug: 63531115
Change-Id: I95dd0c2474f1cd1695ff3083e062ee38867b8a0c