8030048: (fs) Support UserDefinedFileAttributeView/extended attributes on OS X / HFS+

[JaniruTEC]

To whom it may concern,

I was tasked by my employer to fix issue 8030048 and contribute an 
implementation of the XAttr API for MacOS to the JDK.
As outlined in the JDK contribution guidelines this is my request for 
the permission to contribute this change and my query for the current 
state of development if there is any.

Please excuse any missing information as this is my first time 
contributing to the JDK.
If there are any questions, please don't hesitate to contact me.

Kind regards,
JaniruTEC