Rewrite handling of JsonAutoDetect / VisibilityChecker

[cowtowncoder]

Since handling of @JsonAutoDetect predates use of value objects for annotations (used with @JsonFormat for example), it uses its own variation which is unnecessarily complex and limiting: specifically it does not allow as easy merging. But while it'd be nice to rewrite this, update is bit complicated since JAXB annotation introspector uses this as well.

Given this it is perhaps best to rewrite this in 3.x, not in 2.9.

For 2.9, #1347 has added @JsonAutoDetect.Value and some of its uses for overrides. Maybe 3.x can remove need for separate VisibilityChecker, if that makes sense.

[cowtowncoder]

Not 100% sure what I thought here, but if this is just about removing one intermediate class that may well make sense... working in this are now.

[cowtowncoder]

Although simplifications were possible, I think I'll leave separation as-is. Except for one thing: I changed VisibilityChecker to be a non-generic implementation, overridable; this to remove need for api/impl separation that at this point adds no value. Change is in 3.0.