Provide base icon for type alias descriptor.

Use platform icon for a class (as we do for type parameters).

idea/idea-analysis/src/org/jetbrains/kotlin/idea/KotlinDescriptorIconProvider.java

@@ -134,6 +134,10 @@ public final class KotlinDescriptorIconProvider {
             return PlatformIcons.CLASS_ICON;
         }
 
+        if (descriptor instanceof TypeAliasDescriptor) {
+            return PlatformIcons.CLASS_ICON;
+        }
+
         LOG.warn("No icon for descriptor: " + descriptor);
         return null;
     }