RFR: 8223312: Utilize handshakes instead of is_thread_fully_suspended [v2]

[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 incrementally with two additional commits since the last revision:

 - Removed TraceSuspendDebugBits
 - Removed unused method is_ext_suspend_completed_with_lock

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/729/files
  - new: https://git.openjdk.java.net/jdk/pull/729/files/7e77a04f..386b930f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=729&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=729&range=00-01

  Stats: 94 lines in 2 files changed: 0 ins; 88 del; 6 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