Add person name formatting in ICU4X

[sffc]

It would be nice to have an ICU4X implementation of the output of the CLDR Person Names WG, ideally in time for the Unicode person names event.

[sffc]

• @zbraniecki - It may be a bit tricky because the spec is so new and there are probably loose ends.
• @sffc - It's more about the positioning of ICU4X as implementing the latest cutting-edge features.