RFR: 8289284: jdk.tracePinnedThreads output confusing when pinned due to native frame [v2]

[Alan Bateman]

> The system property jdk.tracePinnedThreads triggers a stack trace to be printed when a virtual thread parks while pinned. If a virtual thread is pinned due to a native frame there is a spurious " <== monitors:0" added to line for the native method.
> 
> A secondary issue is that there is no stack trace when there is Panama downcall as there isn't a native method in the stack trace. A future change may annotate the downcalls, for now the entire stack trace is printed (no filtering) so there is at least some output when pinned due to a call through native code

Alan Bateman 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 three additional commits since the last revision:

 - PrintStream can auto flush
 - Merge
 - Initial commit

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9308/files
  - new: https://git.openjdk.org/jdk/pull/9308/files/305b8541..ebbbd985

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9308&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9308&range=00-01

  Stats: 116667 lines in 2199 files changed: 70705 ins; 29043 del; 16919 mod
  Patch: https://git.openjdk.org/jdk/pull/9308.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9308/head:pull/9308

PR: https://git.openjdk.org/jdk/pull/9308