@JsonProperty and equivalents should merge with AnnotationIntrospectorPair

[cowtowncoder]

Describe your Issue

If a property has multiple naming annotations -- such as standard @JsonProperty, and @JacksonXmlProperty from jackson-dataformat-xml -- and there are 2 AnnotationIntrospectors, then AnnotationIntrospectorPair should merge parts so that if the Primary introspector has no value (empty String or null), value from secondary should be used, for:

1. Local name
2. Namespace

so that, for example:

@JacksonXmlProperty(isAttribute=true)
@JsonProperty(namespace="uri:ns1", value="prop")
public int value;

where first annotation has precedence (annotation introspector that handles it is the first introspector configured for AnnotationIntrospectorPair) we should have localName and namespace from @JsonProperty since JacksonXmlProperty defines neither (that is, has defaults of "").
Currently this is not the case.