Locale-aware formatting (but not parsing)

[dkhalanskyjb]

There's no correct multiplatform solution for saying things like "format the current year and month for the Chinese users" or "format the local time the way a user of the current system locale would expect."

Note that Kotlin doesn't provide locale support at all at this moment, and it would probably be strange to have kotlinx.datetime.format.Locale, so we first need to consider the overall locale support in the Kotlin ecosystem.

Since this topic is vast, please share your insights under the corresponding discussion: https://github.com/Kotlin/kotlinx-datetime/discussions/253; this issue is for tracking our progress.