Routing: support routing to a specific element ID (e.g. /home#about) and scrolling to the right place

[sinking-point]

In plain HTML you can link to a specific ID on a page, e.g.

<a href="/home#about">About</a>

This navigates to /home and scrolls to the element with ID about.

There appears to be no way to do a similar thing with RouterAnchor. I have tried doing something like this:

#[derive(Switch, Debug, Clone)]
pub enum AppRoute {
    #[to = "/#{id}"]
    IndexId(String),
    #[to = "/"]
    Index,
}

                    <RouterAnchor<AppRoute> route=AppRoute::IndexId("about".to_owned())>
                        {"About"}
                    </RouterAnchor<AppRoute>>

However, this doesn't scroll to the specified element. It's also unergonomic.

I don't have a full understanding of how the routing works, but I propose having a method in Switch which takes an ID of an element and returns a struct that also implements Switch. The struct would store the ID to scroll to, along with the original Switch-implementing enum value. When a Route is generated from the Switch, the ID is passed through so that the router knows to scroll to the ID.

This would allow syntax like:

<RouterAnchor<AppRoute> route=AppRoute::Index.scroll_to("about")>
    {"About"}
</RouterAnchor<AppRoute>>