RFR: Merge jdk17

[Jesper Wilhelmsson]

Forwardport JDK 17 -> JDK 18

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Commit messages:
 - Merge
 - 8269825: [TESTBUG] Missing testing for x86 KNL platforms
 - 8269955: ProblemList compiler/vectorapi/VectorCastShape[64|128]Test.java tests on x86
 - 8268966: AArch64: 'bad AD file' in some vector conversion tests
 - 8225667: Clarify the behavior of System::gc w.r.t. reference processing
 - 8269568: JVM crashes when running VectorMask query tests
 - 8269661: JNI_GetStringCritical does not lock char array
 - 8269575: C2: assert(false) failed: graph should be schedulable after JDK-8252372
 - 8268883: C2: assert(false) failed: unscheduable graph
 - 8268369: SIGSEGV in PhaseCFG::implicit_null_check due to missing null check

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.java.net/?repo=jdk&pr=4698&range=00.0
 - jdk17: https://webrevs.openjdk.java.net/?repo=jdk&pr=4698&range=00.1

Changes: https://git.openjdk.java.net/jdk/pull/4698/files
  Stats: 3666 lines in 51 files changed: 2827 ins; 351 del; 488 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4698.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4698/head:pull/4698

PR: https://git.openjdk.java.net/jdk/pull/4698