refactor(query-builder): class for mouse drag placeholder class

Author: ivanvpetrov

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

@@ -126,14 +126,12 @@
     <ng-template #operandTemplate let-expressionItem>
         @if (!expressionItem.inEditMode) {
             @if(dragService.dropGhostExpression && expressionItem === dragService.dropGhostExpression && dragService.isKeyboardDrag === false){
-                <!-- TODO style properly -->
-                <div [ngClass]="'igx-filter-tree__expression-item igx-filter-tree__expression-item-drop-ghost'">
+                <div class="igx-filter-tree__expression-item igx-filter-tree__expression-item-drop-ghost igx-filter-tree__expression-item-drop-ghost-placeholder">
                 <igx-chip [data]="expressionItem">
                     {{this.resourceStrings.igx_query_builder_drop_ghost_text}}
                 </igx-chip>
             </div>
-            }
-            @else {
+            } @else {
             <div
                 #dragRef
                 igxDrop