[Magnifier-32] Do not magnify outside selection

Currently, for selection, if we move one handle towards the other, the
moving handle will stop when the selection becomes 1 character long.
However, the magnifier would continue to follow the finger after this,
no longer being helpful for the selection.

This CL fixes this, by replicating what happens when the magnifier
reaches the end of the line also for the case when it reaches the other
handle.

Bug: 72314536
Test: manual testing (both English and Arabic)
Test: atest FrameworksCoreTests:android.widget.TextViewActivityTest
Test: atest CtsWidgetTestCases:android.widget.cts.TextViewTest
Change-Id: I5bde622421c7fb8ecce0ea00f0d8d2af7aa72cf4