Add setBackdropRenderEffect for View and RenderNode.

support visual effects for backdrop contents of a View or RenderNode.

Test: added unit test & hwui_unit passes
Test: added BackdropBlurActivity in HwAccelerationTest, build & run it

Signed-off-by: Dongya Jiang <jiangdongya@coolpad.com>
Change-Id: If1ac1b8aee53667f175e8fa80ecfc7bdfa28173d