RFR: Merge jdk16

[Jesper Wilhelmsson]

Forwardport JDK 16 -> JDK 17

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Commit messages:
 - Merge
 - 8253996: Javac error on jdk16 build 18: invalid flag: -Xdoclint:-missing
 - 8259028: ClassCastException when using custom filesystem with wrapper FileChannel impl
 - 8259043: More Zero architectures need linkage with libatomic
 - 8259429: Update reference to README.md
 - 8259014: (so) ServerSocketChannel.bind(UnixDomainSocketAddress)/SocketChannel.bind(UnixDomainSocketAddress) will have unknown user and group owner (win)

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.java.net/?repo=jdk&pr=2040&range=00.0
 - jdk16: https://webrevs.openjdk.java.net/?repo=jdk&pr=2040&range=00.1

Changes: https://git.openjdk.java.net/jdk/pull/2040/files
  Stats: 140 lines in 12 files changed: 117 ins; 2 del; 21 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2040.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2040/head:pull/2040

PR: https://git.openjdk.java.net/jdk/pull/2040