Made ImageView.animateTransform(Matrix) public

ImageView.animateTransform(Matrix) is now public so we can use it in AndroidX Transitions without a reflection.
Also I fixed a bug that we forgot to clear mDrawMatrix when we provide null matrix into a method. Before it doesn't work as expected if ImageView already calculated some draw matix and we wan't to override it.

Bug: 117521477
Test: Added new cts tests for both usages with null and not null matrix
Change-Id: I9e25e1f673fabdfeb227fabc0b3635056de0a6fd