feat: support Option<_> in style: (closes #3568)

[gbj]

I don't know that I've tested every permutation of these trait implementations, but have tested the following, for example.

#[component]
fn HomePage() -> impl IntoView {
    let count = RwSignal::new(0);

    view! {
        <button
            on:click=move |_| *count.write() += 1
            style:font-weight=move || (count.get() % 2 == 0).then_some("bold")
            style:padding-top=move || format!("{}px", count.get())
            style:text-decoration="underline"
            style="color: red"
        >
            "Click"
        </button>
    }
}