RFR: 8316456: StackWalker may skip Continuation::yield0 frame mistakenly [v3]

[Mandy Chung]

> `JVM_MoreStackWalk` has a bug that always assumes that the Java frame
> stream is currently at the frame decoded in the last patch and so always
> advances to the next frame before filling in the new batch of stack frame.
> However `JVM_MoreStackWalk` may return 0.  The library will set 
> the continuation to its parent. It then call `JVM_MoreStackWalk` to continue
> the stack walking but the last decoded frame has already been advanced.
> The Java frame stream is already at the top frame of the parent continuation. .
> The current implementation skips "Continuation::yield0" mistakenly.  This
> only happens with `-XX:+ShowHiddenFrames` or `StackWalker.Option.SHOW_HIDDEN_FRAMES`.
> 
> The fix is to pass the number of frames decoded in the last batch to `JVM_MoreStackWalk`
> so that the VM will determine if the current frame should be skipped or not.
> 
> `test/jdk/jdk/internal/vm/Continuation/Scoped.java` test now correctly checks
> the expected result where "yield0" exists between "enter" and "run" frames.

Mandy Chung has updated the pull request incrementally with one additional commit since the last revision:

  minor clean up

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15804/files
  - new: https://git.openjdk.org/jdk/pull/15804/files/ddaeaf99..14f13223

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15804&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15804&range=01-02

  Stats: 4 lines in 1 file changed: 0 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15804.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15804/head:pull/15804

PR: https://git.openjdk.org/jdk/pull/15804