De-duplicate method references in java.util.stream.FindOps

When initializing j.u.stream.FindOps$FindRef we spin up some duplicate lambda proxy classes:

            static final TerminalOp<?, ?> OP_FIND_FIRST = new FindOp<>(true,
                    StreamShape.REFERENCE, Optional.empty(),
                    Optional::isPresent, FindSink.OfRef::new);

            static final TerminalOp<?, ?> OP_FIND_ANY = new FindOp<>(false,
                    StreamShape.REFERENCE, Optional.empty(),
                    Optional::isPresent, FindSink.OfRef::new);

Extracting Optional::isPresent and FindSink.OfRef::new to static constants means we can reuse the lambdas for the different streams. A simple, minor startup win.