8260966: (fs) Consolidate Linux and macOS implementations of UserDefinedFileAttributeView

src/java.base/linux/classes/sun/nio/fs/LinuxFileStore.java

src/java.base/linux/classes/sun/nio/fs/LinuxFileSystem.java

....base/linux/classes/sun/nio/fs/LinuxNativeDispatcher.java

...classes/sun/nio/fs/LinuxUserDefinedFileAttributeView.java

src/java.base/linux/native/libnio/fs/LinuxNativeDispatcher.c

src/java.base/macosx/classes/sun/nio/fs/BsdFileStore.java

src/java.base/macosx/classes/sun/nio/fs/BsdFileSystem.java

...a.base/macosx/classes/sun/nio/fs/BsdNativeDispatcher.java

...x/classes/sun/nio/fs/BsdUserDefinedFileAttributeView.java

src/java.base/macosx/native/libnio/fs/BsdNativeDispatcher.c

src/java.base/share/classes/sun/nio/fs/NativeBuffer.java

....base/unix/classes/sun/nio/fs/UnixConstants.java.template

src/java.base/unix/classes/sun/nio/fs/UnixFileStore.java

...va.base/unix/classes/sun/nio/fs/UnixNativeDispatcher.java

.../classes/sun/nio/fs/UnixUserDefinedFileAttributeView.java

src/java.base/unix/native/libnio/fs/UnixNativeDispatcher.c