Improve `FactoryBasedEnumDeserializer` to work better with XML module

[cowtowncoder]

Describe your Issue

(note: this is to help solve FasterXML/jackson-dataformat-xml#682)

It looks like FactoryBasedEnumDeserializer does not have same work-around as basic EnumDeserializer has for Object valued input:

(line 287)

        // 29-Jun-2020, tatu: New! "Scalar from Object" (mostly for XML)
        if (p.isExpectedStartObjectToken()) {
            return _fromString(p, ctxt,
                    ctxt.extractScalarFromObject(p, this, _valueClass));
        }

But it should have, to support String-argument taking "DELEGATING" Creator.
Let's add handling.