PropertyDataFetcher supports AutoValue style classes

[iancw]

Google's AutoValue library (https://github.com/google/auto/)
generates package-protected implementations of abstract
data classes with abstract public getters. These classes
weren't supported by the PropertyDataFetcher, since invoking
the public method on a package-protected class causes
InvocationTargetException. However, invoking the method
on the public parent class works fine.

These changes look for a public parent class with the applicable
getter method. Behavior with normal style classes should not be
affected.

[danielkwinsor]

I did something like this in my repo, I'll look at this.

[dminkovsky]

Hi @iancw. Thanks for this PR!

This appears to be related to #164, which was recently merged.

The conversation on #164 touched upon the extent to which we want to make PropertyDataFetcher support various use-cases at the expense of being a very simple built-in data fetcher. google/auto is probably used quite commonly, but given how easy it is to make one's own data fetchers, I'm not sure it makes sense to extend the very simple built in to cover this scenario. The decision to support various boolean prefixes on #164 was based on repeated community demand.

[bbakerman]

I dont think this is an particularly unusual case. Just more forgiving.

It ascends the class hierarchy and finds the first public method on a the object that comes from a public class. It exactly matches we have today and more.

I think we should merge this.