feat(item): add item-content attr selector

Closes #6643

src/components/item/item.ts

@@ -48,7 +48,7 @@ import {Label} from '../label/label';
         '<ion-label *ngIf="_viewLabel">' +
           '<ng-content></ng-content>' +
         '</ion-label>' +
-        '<ng-content select="ion-select,ion-input,ion-textarea,ion-datetime,ion-range"></ng-content>' +
+        '<ng-content select="ion-select,ion-input,ion-textarea,ion-datetime,ion-range,[item-content]"></ng-content>' +
       '</div>' +
       '<ng-content select="[item-right],ion-radio,ion-toggle"></ng-content>' +
     '</div>' +

src/components/item/test/text/main.html

@@ -48,4 +48,13 @@
     </ion-label>
   </ion-item>
 
+  <ion-item>
+    <ion-label>
+      ion-label
+    </ion-label>
+    <div item-content>
+      [item-content]
+    </div>
+  </ion-item>
+
 </ion-content>