Bring back the 'contains' operator

src/lib/make-toolbox-xml.js

@@ -603,6 +603,18 @@ const operators = `
                 </shadow>
             </value>
         </block>
+        <block type="operator_contains" id="operator_contains">
+          <value name="STRING1">
+            <shadow type="text">
+              <field name="TEXT">hello</field>
+            </shadow>
+          </value>
+          <value name="STRING2">
+            <shadow type="text">
+              <field name="TEXT">world</field>
+            </shadow>
+          </value>
+        </block>
         ${blockSeparator}
         <block type="operator_mod">
             <value name="NUM1">