feat: impl Date API

[amilajack]

Implements neon-bindings/rfcs#18

• impl JsDate::new
• impl JsDate::new_lossy
• impl JsDate::try_new
• impl JsDate::is_date
• impl JsDate::is_valid
• Write tests

[dherman]

Looks good! Just a few minor comments.

[arthrarnld]

Hey peeps. Any news on this one? Having it would be really helpful in our team. Thanks!

[kjvalencik]

@arthrarnld It's a work in progress. We're still discussing the best way to handle an out of range time. Let us know if you have any thoughts! If you need this feature now, it can be implemented outside of Neon.

fn global_date<'a, C: Context<'a>>(cx: &mut C) -> JsResult<'a, JsFunction> {
    cx.global()
        .get(cx, "Date")?
        .downcast::<JsFunction>()
        .or_throw(cx)
}

fn create_date<'a, C: Context<'a>>(
    cx: &mut C,
    n: f64,
) -> JsResult<'a, JsObject> {
    let date = global_date(cx)?;
    let args = vec![cx.number(n)];

    date.construct(cx, args)
}

// Doesn't really validate that it's a date, just that it has a `now()` function
// that returns a `number`. Could validate with `isPrototypeOf`, but probably not worth it.
fn date_value<'a, C: Context<'a>>(
    cx: &mut C,
    o: Handle<JsObject>,
) -> NeonResult<f64> {
    let now = o.get(cx, "now")?.downcast::<JsFunction>().or_throw(cx)?;
    let args = Vec::<Handle<JsValue>>::with_capacity(0);
    let res = now.call(cx, o, args)?.downcast::<JsNumber>().or_throw(cx)?;

    Ok(res.value())
}

[kjvalencik]

@amilajack This looks great! Before merging, let's decide whether we want this feature flagged or not prior to merging the RFC.