Active style for mat-nav-list

There's a theme-specific active style for navigation items in a nav drawer:

https://material.io/design/components/navigation-drawer.html#standard-drawer

(Note the way "inbox" is highlighted, because that's the section we're currently in).

However, there's no way to achieve this style in Angular Material. Ideally, there'd be a way to do this with routerLinkActive on a mat-nav-list.

Start by reviewing the mat-nav-list entry point and how routerLinkActive applies to navigation items, then compare the requested behavior with the linked Material Design navigation-drawer example. Done means Angular Material provides a documented way to show the active navigation section with the requested theme-specific styling.

Written by the indexing model from the issue text.