[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>
diff --git a/skottie/skottie_sample_search.json b/skottie/skottie_sample_search.json
index dddb766..f880f0a 100644
--- a/skottie/skottie_sample_search.json
+++ b/skottie/skottie_sample_search.json
@@ -117,7 +117,7 @@
                             "lc": 2,
                             "lj": 2,
                             "mn": "ADBE Vector Graphic - Stroke",
-                            "nm": "Stroke 1",
+                            "nm": "$Stroke 1",
                             "o": {
                                 "a": 0,
                                 "ix": 4,
@@ -143,7 +143,7 @@
                             },
                             "hd": false,
                             "mn": "ADBE Vector Graphic - Fill",
-                            "nm": "Fill 1",
+                            "nm": "$Fill 1",
                             "o": {
                                 "a": 0,
                                 "ix": 5,
@@ -249,7 +249,7 @@
                             "lc": 1,
                             "lj": 2,
                             "mn": "ADBE Vector Graphic - Stroke",
-                            "nm": "Stroke 1",
+                            "nm": "$Stroke 1",
                             "o": {
                                 "a": 0,
                                 "ix": 4,