* Fix TypeAdapterRuntimeTypeWrapper not detecting reflective TreeTypeAdapter
Previously on serialization TypeAdapterRuntimeTypeWrapper preferred a
TreeTypeAdapter without `serializer` which falls back to the reflective
adapter. This behavior was incorrect because it caused the reflective
adapter for a Base class to be used for serialization (indirectly as
TreeTypeAdapter delegate) instead of using the reflective adapter for
a Subclass extending Base.
* Address review feedback
* Convert TypeAdapterRuntimeTypeWrapperTest to JUnit 4 test
* Prefer wrapped reflective adapter for serialization of subclass
* Detect reflective adapter used as delegate for Gson.FutureTypeAdapter
* Tiny style tweak.
Co-authored-by: Éamonn McManus <emcmanus@google.com>
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