RFR: 8344328: (dc) DatagramChannelImpl.blockingReceive can now synchronize on packet [v2]

[Alan Bateman]

> Now that JEP 491 is integrated, we can restore long-standing behavior in the DatagramSocket adaptor to synchronize on the DatagramPacket for the duration of the send/receive.

Alan Bateman has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - Broadly scope of synchronized blocks
 - Merge branch 'master' into JDK-8344328
 - Merge branch 'master' into JDK-8344328
 - Merge branch 'JDK-8344328'
 - More improvements
 - Initial commit

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Changes:
  - all: https://git.openjdk.org/jdk/pull/22212/files
  - new: https://git.openjdk.org/jdk/pull/22212/files/a50fdddc..ade7ba0b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22212&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22212&range=00-01

  Stats: 5530 lines in 231 files changed: 573 ins; 3896 del; 1061 mod
  Patch: https://git.openjdk.org/jdk/pull/22212.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22212/head:pull/22212

PR: https://git.openjdk.org/jdk/pull/22212