Change Locale handling to use static methods toLanguageTag() and forLanguageTag

[cowtowncoder]

(note: follow up for #1948)

It seems that static methods of Locale:

• toLanguageTag() (for serialization)
• forLanguageTag(String) (for deserialization)

would work better than existing logic, so let's see if we can use those.

Since this is potentially breaking change, regarding backwards compatibility, it can not go in a patch version (2.9.x), but needs to go in 3.0.

[cowtowncoder]

Hmmh. Ok, trouble.

On plus side, serialization already uses toLanguageTag(): no change needed.

On downside, forLanguageTag() does NOT accept underscore at all, it seems, just hyphen.
So it is not really an improvement.

Not sure if there is anything to do... back to the old drawing board.

[cowtowncoder]

Have to shelve for now.

[takeseem]

I hope you can support, because of our app and server are use Java's System and use Jackson json protocol.

at last, we can use -Dsystem.properties to switch back to des Locale like in Jackson v2.7.6.

[cowtowncoder]

@takeseem I don't think this can be done, at all. I do not know of any way to make it work in backwards compatible way, or how change even should work.

If you need such handling I would recommend use of custom serializer and/or deserializer for Locale type.