Fix T61647031 - color comparison causing TextAttribute color to not update ParagraphState

Summary:
As documented in T61647031, Text colors were sometimes not being updated because the ParagraphState was not always updating with a new AttributedString.

Turns out, it's because the equality comparator for Color had not been implemented, and so State was not being set in some cases.

The confusing part is that now color comparisons return true **more often** than before (if you're comparing two smart pointers of opaque data without a custom comparator, in theory I assume they're comparing pointer values and returning false way more often... but maybe my understanding is off). This distracted us for a while in finding an other ~fairly simple solution.

We should keep this in mind if we experience other, similar issues with text attributes not updating.

Changelog: [Internal] Fabric

Reviewed By: mdvacca

Differential Revision: D20300307

fbshipit-source-id: 13d86495f4c4ef8a0219fec66d39a49b4f7e6c2a

ReactCommon/fabric/graphics/platform/cxx/Color.h

@@ -42,6 +42,14 @@ class SharedColor {
     return color_;
   }
 
+  bool operator==(const SharedColor &otherColor) const {
+    return color_ == otherColor.color_;
+  }
+
+  bool operator!=(const SharedColor &otherColor) const {
+    return color_ != otherColor.color_;
+  }
+
   operator bool() const {
     return color_ != UndefinedColor;
   }