[Magnifier-31] Do not magnify outside current line

Currently, after the cursor is reaching the end of a line, the magnifier
keeps following the finger even if the cursor cannot move anymore.

This CL limits the movement of the magnifier, ensuring it stays between
the bounds of the text line. Also, when the finger gets too far from the
end of the line, we dismiss the magnifier. We consider it went too far
when the cursor is not visible anymore inside the magnifier.

Bug: 72314536
Test: manual testing (both English and Arabic)
Test: atest FrameworksCoreTests:android.widget.TextViewActivityTest
Test: atest CtsWidgetTestCases:android.widget.cts.TextViewTest
Change-Id: I8dafba1fc8e7b8e482526e818831ece2ee20ac27