RFR: 8234131: Miscellaneous changes imported from jsr166 CVS 2020-12

[Martin Buchholz]

8234131: Miscellaneous changes imported from jsr166 CVS 2020-12

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Commit messages:
 - JDK-8234131

Changes: https://git.openjdk.java.net/jdk/pull/1647/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1647&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8234131
  Stats: 314 lines in 41 files changed: 107 ins; 41 del; 166 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1647.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1647/head:pull/1647

PR: https://git.openjdk.java.net/jdk/pull/1647