Add Escape key support to the SearchBox of the MudSelectExtended (#460)

Co-authored-by: Peter Chapman <pchapman@micromine.com>

Author: pjc2007

CodeBeam.MudBlazor.Extensions/Components/ListExtended/MudListExtended.razor.cs

@@ -936,6 +936,13 @@ protected internal async Task SearchBoxHandleKeyDown(KeyboardEventArgs obj)
                         await MudSelectExtended.FocusAsync();
                     }
                     break;
+                 case "Escape":                    
+                    if (MudSelectExtended != null && MultiSelection == false)
+                    {
+                        await MudSelectExtended.CloseMenu();
+                        await MudSelectExtended.FocusAsync();
+                    }
+                    break;
                 case "Tab":
                     await Task.Delay(10);
                     await ActiveFirstItem();