For now don't expose this as additional GsonBuilder method assuming that
the default nesting limit is high enough for most users. Otherwise users
can first obtain a JsonReader from `Gson.newJsonReader` and then set a
custom nesting limit.

See comment in JsonTreeReaderTest for the rationale

# Conflicts:
#	gson/src/main/java/com/google/gson/stream/JsonReader.java
#	gson/src/test/java/com/google/gson/internal/bind/JsonTreeReaderTest.java