RFR: Merge jdk16

[Jesper Wilhelmsson]

Forwardport JDK 16 -> JDK 17

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Commit messages:
 - Merge
 - 8259794: Remove EA from JDK 16 version string starting with Initial RC promotion on Feb 04, 2021(B35)
 - 8260704: ParallelGC: oldgen expansion needs release-store for _end
 - 8260927: StringBuilder::insert is incorrect without Compact Strings
 - 8258378: Final nroff manpage update for JDK 16
 - 8257215: JFR: Events dropped when streaming over a chunk rotation
 - 8260473: [vector] ZGC: VectorReshape test produces incorrect results with ZGC enabled
 - 8260632: Build failures after JDK-8253353
 - 8260339: JVM crashes when executing PhaseIdealLoop::match_fill_loop
 - 8260608: add a regression test for 8260370
 - ... and 2 more: https://git.openjdk.java.net/jdk/compare/f025bc1d...dad835ee

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.java.net/?repo=jdk&pr=2392&range=00.0
 - jdk16: https://webrevs.openjdk.java.net/?repo=jdk&pr=2392&range=00.1

Changes: https://git.openjdk.java.net/jdk/pull/2392/files
  Stats: 2645 lines in 56 files changed: 2497 ins; 69 del; 79 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2392.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2392/head:pull/2392

PR: https://git.openjdk.java.net/jdk/pull/2392