fix(blazorui): resolve issue of clear button in BitDropdown when ItemsProvider is used #11083 (#11088)

Author: msynk

src/BlazorUI/Bit.BlazorUI/Components/Inputs/Dropdown/BitDropdown.razor.cs

@@ -1143,6 +1143,8 @@ private async Task HandleOnClearClick()
             if (InvalidValueBinding()) return;
 
             CurrentValue = default;
+
+            _selectedItems.Clear();
         }
 
         UpdateSelectedItemsFromValues();