`@JsonAnyGetter` should be allowed on a field

[cowtowncoder]

(follow-up from FasterXML/jackson-annotations#107)

Would be nice to allow use of @JsonAnyGetter on fields too; javadocs already claim this is possible.
So should add support for allowing that. Note that the counterpart, @JsonAnySetter does allow use on field already.

[cowtowncoder]

While not trivial to implement, this seems like something moderately challenging to implement -- but something users would like to see.

[dominikrebhan]

Hi,

I would like to take this issue. I already lookup up in the code and I think it should be done within the classes @JsonAnyGetter, BasicBeanDescription and POJOPropertiesCollector. The outgoing type of AnnotatedMember is already present and it should be simply extendable for fields.

Best regards.

[cowtowncoder]

@dominikrebhan Go for it! This would be a good improvement.

I think you'll want to start with 2.12 branch (3.0 is too far out, master is tracking that). I just released 2.12.0-rc1, but there is still time -- and if it needs to go against 2.13 due to timing I can help.

[dominikrebhan]

I added the first pull requests. Could you please take a look at a first glance?