[lilliput-jdk17u:lilliput] RFR: 8319897: Move StackWatermark handling out of LockStack::contains

[Roman Kennke]

Backport of https://github.com/openjdk/jdk/commit/bbf52e0e4cb76b4c6425e7d1266dcdbb4df556ea

It's an enhancement to LW locking, backported to keep lockStack code in sync, to ease subsequent backports.

Slightly unclean because of NULL vs nullptr diff.

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Commit messages:
 - 8319897: Move StackWatermark handling out of LockStack::contains

Changes: https://git.openjdk.org/lilliput-jdk17u/pull/78/files
  Webrev: https://webrevs.openjdk.org/?repo=lilliput-jdk17u&pr=78&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319897
  Stats: 17 lines in 2 files changed: 6 ins; 6 del; 5 mod
  Patch: https://git.openjdk.org/lilliput-jdk17u/pull/78.diff
  Fetch: git fetch https://git.openjdk.org/lilliput-jdk17u.git pull/78/head:pull/78

PR: https://git.openjdk.org/lilliput-jdk17u/pull/78