RFR: Merge jdk18

[Jesper Wilhelmsson]

Forwardport JDK 18 -> JDK 19

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Commit messages:
 - Merge remote-tracking branch 'jdk18/master' into Merge_jdk18
 - 8279833: Loop optimization issue in String.encodeUTF8_UTF16
 - 8279370: jdk.jpackage/share/native/applauncher/JvmLauncher.cpp fails to build with GCC 6.3.0
 - 8274007: [REDO] VM Exit does not abort concurrent mark
 - 8279837: C2: assert(is_Loop()) failed: invalid node class: Region

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.java.net/?repo=jdk&pr=7068&range=00.0
 - jdk18: https://webrevs.openjdk.java.net/?repo=jdk&pr=7068&range=00.1

Changes: https://git.openjdk.java.net/jdk/pull/7068/files
  Stats: 124 lines in 6 files changed: 117 ins; 1 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7068.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7068/head:pull/7068

PR: https://git.openjdk.java.net/jdk/pull/7068