Improve ObjectHandler support from user code

[govert]

The ObjectHandler helper should implement a method like

        public static object GetHandle(string callerFunctionName, object callerParameters, Func<object> userObjectFactory)

or should check for this type of argument (not just the internal LazyLambda type) to support user-implement handle wrappers.

We should also implement a nice way to override the handle string that is returned.

[govert]

Prompted by this discussion: https://groups.google.com/g/exceldna/c/WgF2-dg19Yg/m/jX8qjLHTBQAJ