base

Fix Paint Shader copy

- Paint.setClassVariablesFrom(Paint paint) was using the same Shader
for the copy as the initial Paint. Make sure that we are using a copy.
- implement a copy() API for shaders

See bug #7034321 Need Drawable RTL support

Change-Id: I4b9cee386edc72ad670723266333b85f4d2b0ab8