Implement `JsonNodeFeature.READ_NULL_PROPERTIES` to allow skipping of JSON `null` values on reading

[cowtowncoder]

(note: follow up beyond #3405 and part of JSTEP-7)

Now that we have DatatypeFeature capability and newly created JsonNodeFeature, we can start adding more configurability for JsonNode handling. As per JSTEP-7 let's start with

JsonFeature.READ_NULL_PROPERTIES (default: true)

disabling of which allows "dropping" of NullNodes when reading JSON content as JsonNode.