RFR: Merge openjdk/jdk:master

[William Kemper]

Merge tag jdk+21-2 (this includes @ysramakrishna 's fix for `HdrSeq`).

-------------

Commit messages:
 - Merge tag 'jdk-21+2' into merge-jdk21-2
 - 8297639: Remove preventive GCs in G1
 - 8298692: Fix typos in test/jdk/com/sun/jdi files
 - 8296318: use-def assert: special case undetected loops nested in infinite loops
 - 8193547: Regression automated test '/open/test/jdk/java/awt/Toolkit/DesktopProperties/rfe4758438.java' fails
 - 8296610: java/net/HttpURLConnection/SetAuthenticator/HTTPSetAuthenticatorTest.java failed with "BindException: Address already in use: connect"
 - 8298376: ZGC: thaws stackChunk with stale oops
 - 8298475: Remove JVM_ACC_PROMOTED_FLAGS
 - 8298636: Fix return value in WB_CountAliveClasses and WB_GetSymbolRefcount
 - 8298264: Merge OffsetTableContigSpace into TenuredSpace
 - ... and 59 more: https://git.openjdk.org/shenandoah/compare/3901a719...973e99cb

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.org/?repo=shenandoah&pr=187&range=00.0
 - openjdk/jdk:master: https://webrevs.openjdk.org/?repo=shenandoah&pr=187&range=00.1

Changes: https://git.openjdk.org/shenandoah/pull/187/files
  Stats: 10083 lines in 328 files changed: 6622 ins; 2533 del; 928 mod
  Patch: https://git.openjdk.org/shenandoah/pull/187.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah pull/187/head:pull/187

PR: https://git.openjdk.org/shenandoah/pull/187