[css-navigation-1] Add examples (#14012)

* Remove duplicate description

* Add FIXME to disambigue wording

* Change example to have the URL be different from the name

* Add prose and example to clarify how `url-pattern()` patterns work

* Add `url-pattern()` examples that have capture groups

* Move <<route-location>> section to the top

* Extend :link-to() example to also include url() and named route variants

* Move `:active-navigation()` example

* Add simple :active-navigation() example

* Add :active-navigation example with <<navigation-relation>>

* Cater for `url()` including the querystring and the hash when matching

Author: bramus