Replace checked `JsonProcessingException` with unchecked `JacksonException`

[cowtowncoder]

As described in more detail under JSTEP-4, it'd be good to change existing Jackson exception hierarchy (now based on JacksonException, added in 2.12) to extend unchecked RuntimeException instead of checked IOException. This is a major backwards-incompatible change and will need to go in Jackson 3.0.