Improvement - Allow JsonAnyGetter to be used in Map fields

[andrebrait]

Is your feature request related to a problem? Please describe.
Since @JsonAnySetter can be used in fields, I think it would make sense to also allow @JsonAnyGetter to be used in fields whose type is java.util.Map. I fail to see why it shouldn't be able to be used in fields just like @JsonAnySetter is. Considering @JsonAnyGetter only requires the method return type to be java.util.Map, it seems that it's quite intuitive to be able to annotate a field with it.

Describe the solution you'd like
To allow @JsonAnyGetter to be used in fields as well as methods returning java.util.Map.

Usage example
Something like this:

@JsonAnySetter
private final Map<String, Object> aMap = new HashMap<>();

@JsonAnyGetter
public Map<String, Object> getaMap() {
    return this.aMap;
}

could become:

@JsonAnySetter
@JsonAnyGetter
private final Map<String, Object> aMap = new HashMap<>();

Additional context
Opening this more as a request for comments. I might be able to implement this and submit a PR on a later date, if the idea gets approval.

[andrebrait]

For some reason, #1458 didn't show up in my previous query here. Closing this then.