This PR adds a declarative JSON configuration object that allows users to specify the schema of a JSON message. It is meant to have good out-of-the-box defaults, while still allowing power users to modify some of the finer parsing details (should this int field be parseable from a string? should null values be allowed? what if a field is missing? etc). The JSON configuration layer is not tied to any specific implementation; it is introspectible, and could have alternative implementations with other parsing backends. (I could imagine a DHE use-case where they do code-generation based on the JSON configuration, somewhat like the DHE avro ObjectProcessor code generator.)

Out of the box, there's an ObjectProcessor implementation based on the Jackson streaming APIs; that is, the data flows from byte[]s (or InputStream, relevant for very-large-files) to the output WritableChunks without the need for the intermediating Jackson databind layer (TreeNode). This saves a large layer of allocation that our current kafka json_spec layer relies upon. The ObjectProcessor layer means that this can be used in other places that expose ObjectProcessor layers and want 1-to-1 record-to-row (currently, Kafka).

Part of deephaven#5222