(fs) Files.createSymbolicLink should use SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE (win)

A DESCRIPTION OF THE PROBLEM :
Newer builds of Windows 10 with developer mode enabled (and in the future possibly baseline) allow creation of symlinks without elevated privileges by passing the flag SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE (0x2) to the CreateSymbolicLinkW system call. The WindowsFileSystem createSymbolicLink method doesn't pass this flag to the system call, making it fail needlessly when the user doesn't have elevated permissions. Passing the flag when this feature isn't enabled does nothing, so always passing the flag seems like the right thing to do