Update ixdtf to 0.4.0

[Manishearth]

I can't figure out how to construct a fraction, do we need to add APIs upstream?

It may also be worth it to add a direct .to_milliseconds_and_microseconds() API to Fraction.

[Manishearth]

I'm happy to do a quick patch release with the necessary APIs to ixdtf if @nekevss can propose what they should look like

[nekevss]

😕 hmmmmm

So some background: the formatting logic I was potentially going to see if there was any interest in upstreaming into ixdtf, but I hadn't exactly gotten to that point of proposing it. That's the reason the the FormattableX structs exist with some internal ixdtf records.

So baseline a baseline option: we could just remake the functionality in temporal_rs, and live with the differences.

With that being said, if there were any constructor added. It may be a good idea to at minimum upstream the Precision option into ixdtf, then fraction could be something like:

impl Fraction {
    fn from_value_with_precision(value: u64, precision: Option<Precision>)  -> Option<Fraction> {
        match precision {
            None if value == 0 => None,
            None => todo!(), // Derive digit precision from the length of value 
            Some(Precision::Minute) => None,
            Some(Precision::Digit(digit)) => Fraction { digit, value },
        }
    } 
}

Although in this scenario, Precision::Digit would probably need to be a NonZeroU8.

[jedel1043]

Looks great!

[jedel1043]

Will rebase since this also bumps ICU4X, just to see that it merges cleanly.