Make JacksonDeserializer constructor public

[lhazlewood]

The JacksonDeserializer(ObjectMapper objectMapper, Map<String, Class<?>> claimTypeMap) constructor was added as a private constructor in 0.12.4 due to semver constraints.

This issue tracks the work to make that constructor public so devs can still use mapped-type deserialization with their own ObjectMapper instance if desired. This ensures that JJWT does not need to be (regularly) updated any time a particular Jackson deserialization feature/behavior might be preferred - developers can just configure their own ObjectMapper with these features/behaviors.

Note that this needs to be done on 0.13.0 or later due to semver.