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

[Sebastian Stenzel]

This adds support for UserDefinedFileAttributeView on macOS 10.4 and newer.

While the main audience for this will probably be macOS users, the relevant changes take place in (mostly existing) classes carrying BSD in their names as none of this is really macOS-specific.

Code is mostly copied from the Linux implementation except for three differences:
1. max length for attribute names is 127 bytes
2. we know for sure that APFS and HFS+ support extended attributes, therefore we [simply return `true`](https://github.com/skymatic/jdk/blob/7a3619df12853bd3a44e4f49c98f35e15bceb652/src/java.base/macosx/classes/sun/nio/fs/BsdFileStore.java#L114-L118) from `supportsFileAttributeView(UserDefinedFileAttributeView.class)` for these two FS types, while for all other types support is determined experimentally in [`isExtendedAttributesEnabled(...)`](https://github.com/skymatic/jdk/blob/7a3619df12853bd3a44e4f49c98f35e15bceb652/src/java.base/macosx/classes/sun/nio/fs/BsdFileStore.java#L83-L100)
3. For the aforementioned check the new `UnixConstants.ENOATTR` is added, which [seems to be macOS and BSD-specific](https://mail-index.netbsd.org/tech-kern/2012/04/30/msg013090.html).

As discussed in the mailing list, for ease of tracking changes it is not a goal of this patch to modernize the existing Linux implementation, nor to deduplicate anything.

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Commit messages:
 - implemented supportsFileAttributeView
 - Added UserDefinedAttributeView support
 - typo
 - Added JNI methods for fgetxattr/fsetxattr/fremovexattr/flistxattr for BSD

Changes: https://git.openjdk.java.net/jdk/pull/2017/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2017&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8030048
  Stats: 206 lines in 7 files changed: 200 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2017.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2017/head:pull/2017

PR: https://git.openjdk.java.net/jdk/pull/2017