[skottie] Add a custom property manager util class

To facilitate demo code consolidation, introduce a custom property
manager which filters for node names starting with '$' and treats all
properties sharing the same name unitarily.

Update the Colorize GM to use this new helper.

Also revisit the PropertyObserver interface:

 * aliases for client-facing value types
 * introduce a new (decomposed) TransformPropertyValue, to replace component-wise setters
 * consolidate the PropertyHandle interface to only expose get()/set()

Bug: skia:
Change-Id: I9aa9ee80c1fb57bbfbacab0fc3f017da909b24d9
Reviewed-on: https://skia-review.googlesource.com/c/173220
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
1 file changed