RFR: 8173982: (fs) DefaultFileSystemProvider should be split into platform specific versions

[Claes Redestad]

Hi,

sun.nio.fs.DefaultFileSystemProvider can now be implemented directly for 
each platform, removing the need for using reflection.

Since 9 the DefaultFileSystemProvider is initialized on startup, thus 
this indirection can be shown to be cause for a small startup regression 
on unix platforms relative to windows.

Bug: https://bugs.openjdk.java.net/browse/JDK-8173982
Webrev: http://cr.openjdk.java.net/~redestad/8173982/webrev.01/

Thanks!

/Claes