Offer a way to directly set `StreamReadConstraints` via `JsonFactory` (not just Builder)

[cowtowncoder]

Although Builder-style configuration is becoming preferred for Jackson in 2.x (and the only way in 3.0), there is need to support mutable configuration for some key configuration. While for any truly new, optional functionality Builder-style may be sufficient, processing limits change existing behavior so they must be available via "legacy" style configuration too. This is in particular important for frameworks that do not fully control configurability but expose it to their users; and expecting users to change interfaces/mechanisms for ObjectMapper/JsonFactory configuration is a big ask (not to mention compatibility nightmare).

So, before 2.15.0 final, let's ensure StreamReadConstraints can be set on JsonFactory: it can not (alas!) be immutable until 3.0.

[cowtowncoder]

See spring-projects/spring-boot#34709 for context.

[pjfanning]

So if you have an ObjectMapper instance, you can call getFactory() to gets its JsonFactory (which might have been created by the ObjectMapper constructor - or may have been provided when building the ObjectMapper).

The new API will let you reset the StreamReadConstraints on the JsonFactory instance? This would seem like a reasonable solution.

[cowtowncoder]

@pjfanning Correct. Like the way most configuration worked before starting to add Builder-style.