feat: visual distinction between NULL and empty string

Signed-off-by: mertmit <mertmit99@gmail.com>

packages/nc-gui/components/cell/Text.vue

@@ -38,5 +38,7 @@ const focus: VNodeRef = (el) => {
     @mousedown.stop
   />
 
+  <span v-else-if="vModel === null" class="text-gray-300 italic">NULL</span>
+
   <LazyCellClampedText v-else :value="vModel" :lines="1" />
 </template>

packages/nc-gui/components/cell/TextArea.vue

@@ -55,6 +55,8 @@ const rowHeight = computed(() => {
     @mousedown.stop
   />
 
+  <span v-else-if="vModel === null" class="text-gray-300 italic">NULL</span>
+
   <LazyCellClampedText v-else-if="rowHeight" :value="vModel" :lines="rowHeight" />
 
   <span v-else>{{ vModel }}</span>