RFR 8193842: Refactor InputStream-to-OutputStream copy into a utility method

[Brian Burkhalter]

https://bugs.openjdk.java.net/browse/JDK-8194133
http://cr.openjdk.java.net/~bpb/8194133/webrev.00/

Add jdk.internal.io.IOSupport with copy() methods for InputStream-to-OutputStream copying and modify some classes to use these new methods.

One thing that I noticed when looking at this is that in the fix for https://bugs.openjdk.java.net/browse/JDK-8193842, the Files.copy() method had a loop like

while ((n = read(…)) > 0)

whereas InputStream.transferTo() had

while((n = read(…)) >= 0)

which is to say that Files.copy() would terminate if there were an empty read() but transferTo() would not. The patch for 8193842 therefore possibly introduced a subtle behavioral change which no one noticed.

Thanks,

Brian