Allow spread attributes to be set directly

[ealmloff]

Currently, you cannot forward spread attributes through components like this:

#[derive(Props, Clone, PartialEq)]
struct Comp1Props {
    #[props(extends = GlobalAttributes)]
    attributes: Vec<Attribute>,
}

#[component]
fn Comp1(props: Comp1Props) -> Element {
    rsx! {
        Comp2 {
            height: "100%",
            ..props
        }
    }
}

#[derive(Props, Clone, PartialEq)]
struct CompProps2 {
    #[props(extends = GlobalAttributes)]
    attributes: Vec<Attribute>,
}

#[component]
fn Comp2(props: CompProps2) -> Element {
    let attributes = props.attributes;
    rsx! {
        div {
            ..attributes
        }
    }
}

That makes it difficult to build component libraries with many general nested components. This PR implements the simpler fix for spreading attributes through components which lets you set the extends prop directly:

#[derive(Props, Clone, PartialEq)]
struct Comp1Props {
    #[props(extends = GlobalAttributes)]
    attributes: Vec<Attribute>,
}

#[component]
fn Comp1(props: Comp1Props) -> Element {
    rsx! {
        Comp2 {
            attributes: props.attributes.clone(),
            height: "100%",
        }
    }
}

#[derive(Props, Clone, PartialEq)]
struct CompProps2 {
    #[props(extends = GlobalAttributes)]
    attributes: Vec<Attribute>,
}

#[component]
fn Comp2(props: CompProps2) -> Element {
    let attributes = props.attributes;
    rsx! {
        div {
            ..attributes
        }
    }
}

I do think we should look into developing a structural typing system for props, but that will probably not fit into this release. https://docs.rs/frunk/latest/frunk/labelled/trait.Transmogrifier.html looks close to what we would need, but it would require more integration

Fixes #3844