Refine `JacksonModulesRuntimeHints`

[sdeleuze]

[snicoll]

Shouldn't the condition be on a Jackson class? Or the module as it's probably optional.

[sdeleuze]

Good point, I will update accordingly.

[sdeleuze]

In fact, maybe the condition is ok with the builder but we should add a classpath check on the related modules since those are instantiated reflectively.