[OPTIONAL] Consider replacing JSONFormatter with a new PdxJsonObjectMapper

[jxblum]

Currently, the Apache Geode JSONFormatter class (source) and PdxInstance types (e.g. PdxInstanceImpl) has the following problems:

• JSONFormatter cannot handle (top-level) JSON arrays
• JSONFormatter cannot handle JSON type metadata (when activating Jackson ObjectMapper default typing)
• JSONFormatter with PdxInstance(Impl) loses type metadata, id, among other things: Object (using PDX serializer) -> PDX (using JSONFormatter.toJSON(:PdxInstance)) -> JSON (using JSONFormatter.fromJSON(..)) -> PDX (using PdxInstance.getObject()) -> PdxInstance (expect Object here)
• PdxInstance.getObject() cannot handle Java 8 types in general (e.g. Optional), JSR-310 (Time) types in particular, and parameter names even though Jackson does
• I suspect Apache Geode will not work with Jackson 3, which is based on Java 8 by default, due to serialization issues
• PDX is not properly extensible (e.g. you cannot "configure" the static ObjectMapper used by PdxInstanceImpl in the getObject() method, which is blocker issue for many JSON doc types).