CPackWIX: Support CPACK_COMPONENT_<compName>_DISABLED

Reviewed-by: Nils Gladitz <nilsgladitz@gmail.com>

Help/release/dev/wix-disabled-components.rst

@@ -0,0 +1,6 @@
+wix-disabled-components
+-----------------------
+
+* The CPack WIX generator now supports
+  :variable:`CPACK_COMPONENT_<compName>_DISABLED`.
+  This can be used to deselect a component from being installed by default.

Source/CPack/WiX/cmWIXFeaturesSourceWriter.cxx

@@ -86,6 +86,10 @@ void cmWIXFeaturesSourceWriter::EmitFeatureForComponent(
     AddAttribute("Display", "hidden");
   }
 
+  if (component.IsDisabledByDefault) {
+    AddAttribute("Level", "2");
+  }
+
   EndElement("Feature");
 }