[jdk17u-dev] RFR: 8280784: VM_Cleanup unnecessarily processes all thread oops

[Aleksey Shipilev]

Clean backport of performance enhancement for GCs that do concurrent thread roots (in JDK 17u those are Shenandoah and Z). On my machine, with Shenandoah running 20K threads, the safepoint cleanup time for "Cleanup" VM ops dropped from 2ms to nearly zero. A possible follow-up would be [JDK-8280817](https://bugs.openjdk.org/browse/JDK-8280817), which would extend this to other "empty" ops.

Additional testing:
 - [x] Ad-hoc benchmarks
 - [x] Linux x86_64 fastdebug `tier1`, `tier2` 
 - [x] Linux x86_64 fastdebug `tier1`, `tier2`  with `-XX:+DeoptimizeALot`
 - [ ] Linux x86_64 fastdebug `tier1`, `tier2`  with `-XX:+UseShenandoahGC`

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Commit messages:
 - Backport 8a3cca09ba427282f2712bec7298b85bbacf076b

Changes: https://git.openjdk.org/jdk17u-dev/pull/889/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=889&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8280784
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/889.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/889/head:pull/889

PR: https://git.openjdk.org/jdk17u-dev/pull/889