RFR: 8332154: Memory leak in SynchronousQueue [v4]

[Viktor Klang]

> Local testing seems to indicate that this fix (which mirrors what's done in the FIFO mode) addresses the problem. Regression test added for JDK20+

Viktor Klang has updated the pull request incrementally with one additional commit since the last revision:

  Addressing review feedback

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19271/files
  - new: https://git.openjdk.org/jdk/pull/19271/files/cc0a2014..f32e9ea4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19271&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19271&range=02-03

  Stats: 37 lines in 1 file changed: 2 ins; 10 del; 25 mod
  Patch: https://git.openjdk.org/jdk/pull/19271.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19271/head:pull/19271

PR: https://git.openjdk.org/jdk/pull/19271