feat(query-builder): show condition name in tooltip on unary conditions

Author: igdmdimitrov

projects/igniteui-angular/src/lib/query-builder/query-builder-tree.component.html

@@ -136,7 +136,7 @@ <h6 class="igx-filter-empty__title">
                         expressionItem.expression.searchTree.returnFields :
                         expressionItem.expression.searchVal ?
                             expressionItem.expression.searchVal :
-                            null
+                            getConditionFriendlyName(expressionItem.expression.condition.name)
                 }}
             </div>
             <div