RFR 8016324: filter/flatMap pipeline sinks should pass size information to downstream sink

[Paul Sandoz]

Hi,

Please review the following patch contributed by Brian Goetz:

  http://cr.openjdk.java.net/~psandoz/tl/JDK-8016324-pipelines/webrev/

This syncs most of code in the pipeline implementations from lambda to tl (the remaining aspects are to do with Comparator changes which will follow later). 

This patch fixes a bug for the filter and flatMap operations, where the corresponding Sink implementations that were incorrectly reporting size to downstream Sinks. A filter or flatMap might result in the output stream containing a different number of elements to that of the input stream so we have to say to a downstream sink "I don't know what my size will be".

Paul.