RFR: 8373253: Re-work InjectGCWorkerCreationFailure for future changes [v3]

[Leo Korinth]

> This PR slightly changes when we may `InjectGCWorkerCreationFailure`.  At the moment we wait until `is_init_completed()`. I am changing this to instead be after `_created_workers > 0`. The reason is that we might in the future, https://bugs.openjdk.org/browse/JDK-8367993,  create even more threads "on demand", and if so, we would fail VM creation if we inject worker creation failures after the VM is initiated but before we have created any of the worker threads.
> 
> This change should not change the current behaviour. But help future improvements.
> 
> I have tested this on `test/hotspot/jtreg/gc/stress/gcold/TestGCOldWithG1.java`, the only place where this flag is tested to my knowledge.

Leo Korinth 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:

 - Merge branch 'master' into _8373253
 - Fixup after comment from Ivan.
 - 8373253: Re-work InjectGCWorkerCreationFailure for future changes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28719/files
  - new: https://git.openjdk.org/jdk/pull/28719/files/2aa8aa4b..11649b67

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28719&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28719&range=01-02

  Stats: 130210 lines in 3962 files changed: 83748 ins; 29714 del; 16748 mod
  Patch: https://git.openjdk.org/jdk/pull/28719.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28719/head:pull/28719

PR: https://git.openjdk.org/jdk/pull/28719