RFR: Merge jdk16

[Jesper Wilhelmsson]

Forwardport JDK 16 -> JDK 17

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Commit messages:
 - Merge
 - 8259271: gc/parallel/TestDynShrinkHeap.java still fails "assert(covered_region.contains(new_memregion)) failed: new region is not in covered_region"
 - 8259775: [Vector API] Incorrect code-gen for VectorReinterpret operation
 - 8227695: assert(pss->trim_ticks().seconds() == 0.0) failed: Unexpected partial trimming during evacuation
 - 8255199: Catching a few NumberFormatExceptions in xmldsig
 - 8247619: Improve Direct Buffering of Characters

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.java.net/?repo=jdk&pr=2207&range=00.0
 - jdk16: https://webrevs.openjdk.java.net/?repo=jdk&pr=2207&range=00.1

Changes: https://git.openjdk.java.net/jdk/pull/2207/files
  Stats: 131 lines in 11 files changed: 111 ins; 4 del; 16 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2207.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2207/head:pull/2207

PR: https://git.openjdk.java.net/jdk/pull/2207