Add workload that toggles blur behind

Also:
* Add plumbing for specifying a background blur on a scene node
* Add a concept of a properties functor, which is intended to allow for
  animating scene properties without drawing any content
* Add helper for drawing a solid color

Bug: 405591499
Flag: EXEMPT test only
Test: run apk
Change-Id: Ie4e28985afa361e084675bb68f81ec3fed37257b