fix: impl IntoView for Rc<dyn Fn() -> impl IntoView>

[Baptistemontan]

While moving to v0.5.0-rc1 for one of my project I realised I made a mistake with #1669, there is a IntoView impl for Fn() -> impl IntoView but it does not affect Rc<dyn Fn() -> impl IntoView>, so ChildrenFn does not impl IntoView anymore.

// works
let children: Children = ...;
view! { <b>{children}</b> };

// works
let children_mut: ChildrenFnMut = ...;
view! { <b>{children}</b> };

// fail
let children_fn: ChildrenFn = ...;
view! { <b>{children}</b> };
// need to call it to make it work:
view! { <b>{children()}</b>

This PR add a IntoView impl for Rc<dyn Fn() -> impl IntoView>

[gbj]

Thanks!