Ahead-of-time compilation of messages

[amannn]

Is your feature request related to a problem? Please describe.

First results from icu-to-json show, that messages can be compiled to an ultra-slim AST (or even just a plain string—in the case of plain strings) that has very little overhead in comparison to passing raw messages to the client side.

The benefits are:

• Faster message formatting at runtime
• No parsing on the client side / at runtime

Describe the solution you'd like

Switch out intl-messageformat for icu-to-json and make sure the parser only runs on the server side (potentially cached) / at compile time.

Describe alternatives you've considered

Sticking with intl-messageformat.