RFR: 8223312: Utilize handshakes instead of is_thread_fully_suspended [v4]

[Robbin Ehn]

> The main point of this change-set is to make it easier to implement S/R on top of handshakes.
> Which is a prerequisite for removing _suspend_flag (which duplicates the handshake functionality).
> But we also remove some complicated S/R methods.
> 
> We basically just put in everything in the handshake closure, so the diff just looks much worse than what it is.
> 
> TraceSuspendDebugBits have an ifdef, but in both cases it now just returns.
> But I was unsure if I should remove now or when is_ext_suspend_completed() is removed.
> 
> Passes multiple t1-5 runs, locally it passes many jck:vm/nsk_jvmti/nsk_jdi/jdk-jdi runs.

Robbin Ehn has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains ten commits:

 - Merge
 - Review updates
 - Fixed merge miss
 - Merge branch 'master' into 8223312-Utilize-handshakes-instead-of-is_thread_fully_suspended
 - Merge fix from Richard
 - Merge branch 'master' into 8223312-Utilize-handshakes-instead-of-is_thread_fully_suspended
 - Removed TraceSuspendDebugBits
 - Removed unused method is_ext_suspend_completed_with_lock
 - Utilize handshakes instead of is_thread_fully_suspended

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Changes: https://git.openjdk.java.net/jdk/pull/729/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=729&range=03
  Stats: 611 lines in 6 files changed: 174 ins; 376 del; 61 mod
  Patch: https://git.openjdk.java.net/jdk/pull/729.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/729/head:pull/729

PR: https://git.openjdk.java.net/jdk/pull/729