RFR: 8295871: G1: Use different explicit claim marks for CLDs [v2]

[Thomas Schatzl]

> Hi all,
> 
>   can I have reviews for this follow-up to [JDK-8295118](https://bugs.openjdk.org/browse/JDK-8295118) that removes the need to clear CLD claim marks for every full gc phase by using different claim values for the different phases.
> 
> Some comments:
> * I used new g1 specific claim values instead of overloading the existing ones, which is imho clearer. I am open to better names, but something like `_claim_strong_2/3` seemed too cryptic. Then again, there is now a collector specific name in the enum. Maybe the enum values should be made collector-specific in some way? Currently they already are (e.g. `_claim_finalizable` is only used in ZGC) as G1 does not need the values except for (multiple) `_claim_strong`.
> * I moved the CLD mark verification for the mark phase from `prepare_collection` to the constructor of `G1FullGCMarker`; I think this place is more fitting as directly above there is the use in the `CLDToOopClosure`. Also this pattern aligns with the use in the `G1FullGCAdjustTask`.
> 
> Testing: tier1-5
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:

  rename claim bits

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10989/files
  - new: https://git.openjdk.org/jdk/pull/10989/files/8631a235..48c96fc4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10989&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10989&range=00-01

  Stats: 21 lines in 6 files changed: 5 ins; 3 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/10989.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10989/head:pull/10989

PR: https://git.openjdk.org/jdk/pull/10989