fix(aio): smoother transition from page with SideNav to homepage (#17312)

When navigating from a page with open SideNav to a page without closed SideNav,
the main content area animates from a non-zero left margin to zero left margin.
Additionally, the top-bar on the homepage is transparent, which allows the white
background behind the main content to be seen while the left margin is animated
to zero, making it appear as if something (e.g. the SideNav covers the top-bar).

This commit works around this issue, by not making the top-bar transparent
immediately when navigating to the homepage, but animating it from its blue
color to transparent with a delay.

Fixes #17248

aio/src/styles/1-layouts/_top-menu.scss

@@ -53,6 +53,7 @@ aio-top-menu {
 // HOME PAGE OVERRIDE: TOPNAV TOOLBAR HAMBURGER MENU
 aio-shell.page-home md-toolbar.app-toolbar.mat-toolbar {
   background-color: transparent;
+  transition: background-color .2s linear .3s;
 
   @media (max-width: 480px) {
     background-color: $blue;