Allow use of `@JsonCreator(mode = Mode.PROPERTIES)` creator for POJOs with "empty String" coercion

[cowtowncoder]

(note: offshoot of FasterXML/jackson-dataformat-xml#547)

Currently it is possible to allow coercion from JSON Empty String into POJOs that have "default" (aka "no-arg" or "0-arg") Creator (constructor of rfactory method). But it is not possible to use "properties"-style Creator like:

class Pojo {
   protected int a, b;

   @JsonCreator(mode = Mode.PROPERTIES)
   public Pojo(@JsonProperty("a") int a, @JsonProperty("b") int b) {
      this.a = a;
      this.b = b;
   }
}

as deserialization only wants to use default creator.

But we could actually use Properties-passing one (if one exists). Let's allow this.

NOTE: this is most useful for XML use case.