RFR: JDK-8296149: Start of release updates for JDK 21 [v5]

[Joe Darcy]

> Usual start-of-release updates. Symbol updates in initial version reflect JDK 20 build 21.

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Respond to review feedback; reformat test.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10924/files
  - new: https://git.openjdk.org/jdk/pull/10924/files/e252e83a..fc28c49a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10924&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10924&range=03-04

  Stats: 11 lines in 1 file changed: 0 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/10924.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10924/head:pull/10924

PR: https://git.openjdk.org/jdk/pull/10924