RFR: 8253481: Shenandoah: ShenandoahConcurrentRootScanner::oops_do() should always use _claim_strong for CLDClosure

[Zhengyu Gu]

_claim_none should only be used for single thread scanning, regardless concurrent or not.

 ShenandoahConcurrentRootScanner declares ShenandoahClassLoaderDataRoots multi-thread capable, so should always use
 _claim_strong for scanning CLDG.

This is not a correctness bug. _claim_none results CLDG to be scanned by every worker.

Test:
  - [x] hotspot_gc_shenandoah

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

Commit messages:
 - 8253481: Shenandoah: ShenandoahConcurrentRootScanner::oops_do() should always use _claim_strong for CLDClosure

Changes: https://git.openjdk.java.net/jdk/pull/304/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=304&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253481
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/304.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/304/head:pull/304

PR: https://git.openjdk.java.net/jdk/pull/304