Always show variant tag in niche-layout enums

Prior to this, we only showed the `[variant]` synthetic property when
the dataful variant is active. With this change, we now always show it
so the behavior is consistent.

Author: wesleywiser

src/etc/natvis/intrinsic.natvis

@@ -203,6 +203,9 @@
       <Synthetic Condition="is_dataful()" Name="[variant]">
         <DisplayString>{"$T4",sb}</DisplayString>
       </Synthetic>
+      <Synthetic Condition="!is_dataful()" Name="[variant]">
+        <DisplayString>{discriminant,en}</DisplayString>
+      </Synthetic>
     </Expand>
   </Type>
 </AutoVisualizer>