RFR: 8340401: DcmdMBeanPermissionsTest.java and SystemDumpMapTest.java fail with assert(_stack_base != nullptr) failed: Sanity check [v6]

[Simon Tooke]

> This PR addresses JDK-8340401 by adding a test for a thread with no stack currently assigned.

Simon Tooke has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains nine additional commits since the last revision:

 - Merge branch 'pr_windows_system_dump_fixes' of https://github.com/stooke/jdk into pr_windows_system_dump_fixes
 - Merge branch 'openjdk:master' into pr_windows_system_dump_fixes
 - Merge branch 'openjdk:master' into pr_windows_system_dump_fixes
 - Merge branch 'openjdk:master' into pr_windows_system_dump_fixes
 - 8340401: test for thread with uninitialized stack
 - JDK-8340401: also fix spelling in comment
 - test for thread with no stack assigned
 - revert legend fix (will be in a different PR)
 - update legend text for 'offset'

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/21091/files
  - new: https://git.openjdk.org/jdk/pull/21091/files/071bd4ae..f8f8bbab

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21091&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21091&range=04-05

  Stats: 6 lines in 1 file changed: 2 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/21091.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21091/head:pull/21091

PR: https://git.openjdk.org/jdk/pull/21091