Customization for Jackson ObjectMapper

[gmethvin]

(Moved from playframework/playframework#6333)

Json.parse and Json.stringify currently don't allow any customization for how values are converted to and from JsValue. In some cases one may want to do that. For example, one may want to pretty-print the JSON value in dev mode but not in production.

[marcospereira]

@gmethvin I wonder if we should move play.libs.Json (Java API) from playframework/playframework to here. It offers a way to customize the application default ObjectMapper and this can be used by JacksonJson.

WDYT?

[mkurz]

Because this issue was originally moved from the Play repo itself I want to add when using Play JSON via a Play application that
thanks to playframework/playframework#12662 also the Play JSON objectmapper used in Json.parse, Json.stringify, etc. can now be configured via the pekko.serialization.jackson.play {} config key. Plus: A Play app can now also configure the Play JSON standalone specific settings via play.json {} (which when using Play JSON standalone can only be set via system properties).

I keep this open though because when using Play JSON standalone this is not possible right now (Play is using private[play] methods in play-json to set things up)