Translation: Coat layer should affect emission

The standard_surface coat parameters are currently affecting the
baseColor of UsdPreviewSurface. It should also affect emission color.

libraries/bxdf/translation/standard_surface_to_usd.mtlx

@@ -80,10 +80,14 @@
     </dot>
 
     <!-- Emissive -->
-    <multiply name="emissiveColor" type="color3">
+    <multiply name="scaledEmissionColor" type="color3">
       <input name="in1" type="color3" interfacename="emission_color" />
       <input name="in2" type="float" interfacename="emission" />
     </multiply>
+    <multiply name="emissiveColor" type="color3">
+      <input name="in1" type="color3" nodename="scaledEmissionColor" />
+      <input name="in2" type="color3" nodename="coatAttenuation" />
+    </multiply>
 
     <!-- Opacity -->
     <convert name="opacityVector" type="vector3">