Don't apply id keyframes when mix value is 0

Addresses an issue where mixing animations of a nested artboard from it's parent artboard can produce unexpected results when dealing with id based keyframes (such as active solo or draw rules). The proposed solution ignores applying an id keyframe's value to an object if the mix value for that animation/keyframe is 0. This provides a way to turn "off" an id based keyframe during a mix.

Behavior AFTER this update. This example has an artboard with 2 animations that each have different values for active solo and a draw rule that is on or off. This artboard is nested in another artboard which sets the animation mix as seen in the recording.

https://github.com/rive-app/rive/assets/186340/b67e98c8-ab7c-4a92-ab3b-65d27b0eadbd

Behavior BEFORE:

https://github.com/rive-app/rive/assets/186340/c0a6c558-efc4-43ec-8974-57bf8f6ab3e8

Diffs=
b9382846d Don't apply id keyframes when mix value is 0 (#5960)

Co-authored-by: Philip Chung <philterdesign@gmail.com>

.rive_head

@@ -1 +1 @@
-f96c86fcc800a1fa2bec3e97be00cab395ea838d
+b9382846d3152fd87ee8ffc8e7a86ea2b5933a9b

src/animation/keyframe_id.cpp

@@ -5,7 +5,9 @@ using namespace rive;
 
 void KeyFrameId::apply(Core* object, int propertyKey, float mix)
 {
-    CoreRegistry::setUint(object, propertyKey, value());
+    if (mix > 0) {
+        CoreRegistry::setUint(object, propertyKey, value());
+    }
 }
 
 void KeyFrameId::applyInterpolation(Core* object,
@@ -14,5 +16,7 @@ void KeyFrameId::applyInterpolation(Core* object,
                                     const KeyFrame* nextFrame,
                                     float mix)
 {
-    CoreRegistry::setUint(object, propertyKey, value());
+    if (mix > 0) {
+        CoreRegistry::setUint(object, propertyKey, value());
+    }
 }

src/animation/keyframe_string.cpp

@@ -5,7 +5,9 @@ using namespace rive;
 
 void KeyFrameString::apply(Core* object, int propertyKey, float mix)
 {
-    CoreRegistry::setString(object, propertyKey, value());
+    if (mix > 0) {
+        CoreRegistry::setString(object, propertyKey, value());
+    }
 }
 
 void KeyFrameString::applyInterpolation(Core* object,
@@ -14,5 +16,7 @@ void KeyFrameString::applyInterpolation(Core* object,
                                         const KeyFrame* nextFrame,
                                         float mix)
 {
-    CoreRegistry::setString(object, propertyKey, value());
+    if (mix > 0) {
+        CoreRegistry::setString(object, propertyKey, value());
+    }
 }