TASK: Sync z-index values with neos-ui

In the neos-ui we are adopting some z-index values to have more flexibility. To be in sync we should changed it here as well.

@see neos/neos-ui#3289

Neos.Neos/Resources/Private/Styles/_CSSVariables.scss

@@ -54,21 +54,21 @@
   --transition-Slow: 0.5s;
 
   --zIndex-SecondaryToolbar-LinkIconButtonFlyout: 1;
-  --zIndex-FlashMessageContainer: 6;
-  --zIndex-LoadingIndicatorContainer: 5;
+  --zIndex-FlashMessageContainer: 60;
+  --zIndex-LoadingIndicatorContainer: 50;
   --zIndex-SecondaryInspector-Context: 1;
   --zIndex-SecondaryInspector-Iframe: 2;
   --zIndex-SecondaryInspector-Close: 3;
   --zIndex-SecondaryInspectorElevated-Context: 1;
   --zIndex-SecondaryInspectorElevated-DropdownContents: 2;
   --zIndex-Dialog-Context: 1;
   --zIndex-FullScreenClose-Context: 1;
-  --zIndex-Drawer-Context: 1;
+  --zIndex-Drawer: 45;
   --zIndex-Bar-Context: 1;
-  --zIndex-PrimaryToolbar: 4;
+  --zIndex-PrimaryToolbar: 40;
   --zIndex-CheckboxInput-Context: 1;
   --zIndex-DropdownContents-Context: 1;
-  --zIndex-SelectBoxContents: 3;
+  --zIndex-SelectBoxContents: 40;
   --zIndex-NotInlineEditableOverlay-Context: 1;
   --zIndex-CalendarFakeInputMirror-Context: 1;
   --zIndex-RdtPicker-Context: 1;