JacksonJsonSerializer should accept ObjectMapper

Suggested release note text:

You can now create a custom `JacksonJsonSerializer` from an `ObjectMapper`. Previously, you could only use a `JsonMapper`. This makes it easier to use an ObjectMapper created by another component, like Spring Boot. Note: The ObjectMapper must use the JSON data format.

In version 1.0.0, JacksonJsonSerailizer requires a JsonMapper (a subclass of ObjectMapper, specialized for JSON).

For compatibility with frameworks like Spring Boot that use an ObjectMapper instead of JsonMapper, we should let users create a JacksonJsonSerializer from an ObjectMapper.