RFR 8187631 : Refactor FileDescriptor close implementation

[Roger Riggs]

In anticipation of the re-opening (not yet) of the JDK 10 repo please 
review refactoring
the handling of closing of files in FileInputStream, FileOutputStream, 
RandomAccessFile,
and FileChannelImpl and related native code.

The refactoring enables a future improvement to use the cleaner to close 
raw fds
when the FileDescriptors becomes unreferenced.
Webrev:
   cr.openjdk.java.net/~rriggs/webrev-fd-refactor-8187631/

Issue:
  https://bugs.openjdk.java.net/browse/JDK-8187631

Thanks, Roger