Docs: confusion between JsonMapper and ObjectMapper

[mikehearn]

Issue description

The Micronaut Core docs tell you to use JsonMapper instead of Jackson's ObjectMapper as the right interface for serializing objects, but:

1. Micronaut Serialization docs make no mention of this. It says to use ObjectMapper
2. Clicking the first JsonMapper link takes you to a Javadoc for Jackson's ObjectMapper class.
3. The second JsonMapper link works.

Should be a simple docs fix but ... which interface should I use? The Core and Serialization modules don't seem to agree.

[graemerocher]

using JsonMapper lets you switch between Jackson Databind and Micronaut Serialization all other variations do not. So the answer depends if you want to couple yourself to one of the implementations or not