[Meta-Task] Implement Intl using ICU (enables Intl on xplat) and provide a compilation option

[dilijev]

Windows Globalization does not work on xplat targets, so we will re-implement Intl using ICU to allow Intl to work on xplat. Additionally, a compilation option will make this implementation available as an option on Windows as well.

(I've referred to this work item on other issues, but only now realized we didn't have an issue tracking it. So, here it is!)

This meta-task and all subtasks are being tracked in the Intl Project.