[Magnifier - 1] Initial implementation and wiring

* implementation of a magnifier which can be attached to any view
* important APIs:
** show(float centerXOnScreen, float centerYOnScreen, float scale)
** dismiss()
* smart offset => shows below if there is no space above
* controlled by boolean flag (easy to turn off)
* attached the magnifier to Editor's handles
* vertically snaps to the middle of the line containing the
  selection
* horizontally snaps to the offset of the character where
  the selection starts/ends

Bug: 66657373
Test: bit FrameworksCoreTests:android.widget.TextViewActivityTest
Test: bit CtsWidgetTestCases:android.widget.cts.TextViewTest
Test: manual test that shows the magnifier working
Change-Id: I1d4616b8bb1210d869ac47dca137ea9636355250