XWIKI-18712: Properties of type number and text are always empty

See vuejs/vue#12102

Author: manuelleduc

xwiki-platform-core/xwiki-platform-livedata/xwiki-platform-livedata-webjar/src/main/vue/displayers/BaseDisplayer.vue

@@ -44,7 +44,7 @@
           However, this is useful if a custom displayer only implement
           its Editor widget, as a default Viewer widget would still be provided
         -->
-        {{ value }}
+        <span>{{ value }}</span>
       </slot>
     </div>