Animation of percent property values (e.g. pie charts) not working #2099

Normally, a value in preferred units can be parsed back in a cycle.  This is not the case for percent values.  The preferred values range on [0, 1] whereas they are parsed as implicitly having `%` at the end if just a number is specified.  Consider for v4 changing parsing for percent values s.t. unitless values range on [0, 1] and values with `%` range on [0, 100].  For now, just add a case for percent units to use `value` instead of `pfValue`.

src/core/animation/ease.js

@@ -26,6 +26,18 @@ function getEasedValue( type, start, end, percent, easingFn ){
   return val;
 }
 
+function getValue( prop, spec ){
+  if( prop.pfValue != null || prop.value != null ){
+    if( prop.pfValue != null && (spec == null || spec.type.units !== '%') ){
+      return prop.pfValue;
+    } else {
+      return prop.value;
+    }
+  } else {
+    return prop;
+  }
+}
+
 function ease( startProp, endProp, percent, easingFn, propSpec ){
   let type = propSpec != null ? propSpec.type : null;
 
@@ -35,19 +47,8 @@ function ease( startProp, endProp, percent, easingFn, propSpec ){
     percent = 1;
   }
 
-  let start, end;
-
-  if( startProp.pfValue != null || startProp.value != null ){
-    start = startProp.pfValue != null ? startProp.pfValue : startProp.value;
-  } else {
-    start = startProp;
-  }
-
-  if( endProp.pfValue != null || endProp.value != null ){
-    end = endProp.pfValue != null ? endProp.pfValue : endProp.value;
-  } else {
-    end = endProp;
-  }
+  let start = getValue( startProp, propSpec );
+  let end = getValue( endProp, propSpec );
 
   if( is.number( start ) && is.number( end ) ){
     return getEasedValue( type, start, end, percent, easingFn );