[DEV-6947] Add template to match UI values

The UI values need to match AND the question needs to be
visible. We do not have the visibility classifications yet, so we need to
define externs to allow this to build.

core/ui.xml

@@ -109,7 +109,6 @@
         <set cmp="lte" />
       </for-each>
 
-
       <template name="_match-ui-{@cmp@}_"
                 desc="Match UI value {@cmp@}">
         <param name="@on@" desc="Question id" />
@@ -127,6 +126,31 @@
           </match>
         </all>
       </template>
+
+      <template name="_match-extern-ui-{@cmp@}_"
+                desc="Match UI value {@cmp@} - using externs">
+        <param name="@on@" desc="Question id" />
+        <param name="@value@" desc="Match against variable" />
+
+        <param name="@__yields@" desc="Generated visibility yields name">
+          <text>__isvis</text>
+          <param-value name="@on@" rmunderscore="true" lower="true" />
+        </param>
+
+        <extern name="ui_q_{@on@}" type="param" dtype="integer" dim="1" />
+        <extern name="@__yields@" type="cgen" dtype="boolean" dim="1" />
+
+        <all>
+          <match on="@__yields@" />
+
+          <match on="ui_q_{@on@}">
+            <dyn-node name="c:{@cmp@}">
+              <c:value-of name="@value@" />
+            </dyn-node>
+          </match>
+        </all>
+      </template>
     </inline-template>
   </section>
 </package>
+