Normative: Adding Intl.DisplayNames specification.

[FrankYFTang]

Fixes #31.

Based on https://github.com/tc39/proposal-intl-displaynames which is ready for Stage 4.

[FrankYFTang]

We need to address the issue @anba raised about "Conformance" section in this PR
tc39/proposal-intl-displaynames#78

[leobalter]

As my review got too verbose, I'd like to bring back a pending feedback from @anba:

https://tc39.es/ecma402/#conformance lists options which are allowed to have implementation-defined behaviour. For Intl.DisplayNames, the "style" and "type" options should probably be listed there. I'm not yet sure if it makes sense to allow implementation-defined behaviour for the "fallback" option, because I don't exactly know what other kind of fallback should happen here.

@FrankYFTang I've got some minor suggestions, all editorial which I can apply (probably tomorrow).

I can also help on the missing conformance part, please let me know!

[FrankYFTang]

@FrankYFTang I've got some minor suggestions, all editorial which I can apply (probably tomorrow).

Thanks. Great !

I can also help on the missing conformance part, please let me know!

That will be nice.

[leobalter]

Ok, the conflicts are resolved and I'll take a look at this conformance part. I believe it's best to do in a follow up PR we work through this week.

[FrankYFTang]

Ok, the conflicts are resolved and I'll take a look at this conformance part. I believe it's best to do in a follow up PR we work through this week.

Agree