Resolve "Move sub_nav content above the content-wrapper class"

This MR moves the sub_nav content above the sidebar so that the sub_nav can be full-width without resorting to hacks. This is necessary prerequisite for !10096 (merged)

Closes #29880 (closed)

app/assets/stylesheets/framework/nav.scss

@@ -416,14 +416,16 @@
 
 .page-with-layout-nav {
   .right-sidebar {
-    top: ($header-height * 2) + 2;
+    top: ($header-height + 1) * 2;
   }
 
-  .build-sidebar {
-    top: ($header-height * 3) + 3;
+  &.page-with-sub-nav {
+    .right-sidebar {
+      top: ($header-height + 1) * 3;
 
-    &.affix {
-      top: 0;
+      &.affix {
+        top: 0;
+      }
     }
   }
 }