[jdk17] RFR: 8268888: Upstream 8268230: Foreign Linker API & Windows user32/kernel32: String conversion seems broken

[Jorn Vernee]

Upstream fix for 8268230 to mainline JDK.

Prior review thread can be found here: https://github.com/openjdk/panama-foreign/pull/554

Testing: jdk_foreign test suite on Windows and Linux (WSL).

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Commit messages:
 - 8268230: Foreign Linker API & Windows user32/kernel32: String conversion seems broken
 - 8268633: CLinker::toJavaString doesn't check for NULL address

Changes: https://git.openjdk.java.net/jdk17/pull/77/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17&pr=77&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268888
  Stats: 315 lines in 6 files changed: 148 ins; 154 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk17/pull/77.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17 pull/77/head:pull/77

PR: https://git.openjdk.java.net/jdk17/pull/77