RFR: 8372250: Merge PtrQueue into SATBMarkQueue

[Ben Taylor]

This change merges `PtrQueue` into its only child class, `SATBMarkQueue`. The corresponding `PtrQueueSet` is merged with `SATBMarkQueueSet`, and `G1SATBMarkQueueSet` and `ShenandoahSATBMarkQueueSet` continue to inherit from that class.

There are few code modifications - most methods were moved directly from `PtrQueue` to `SATBMarkQueue`. The one meaningful change is to  preserve `SATBMarkQueue`'s call to `filter(queue);` before `flush_queue`. 

This change passes all tier1 jtreg tests with both Shenandoah and G1 in local testing.

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Commit messages:
 - Additional jcheck whitespace fix
 - Fix missing includes and whitespace in previous commit
 - 8372250: Merge PtrQueue into SATBMarkQueue

Changes: https://git.openjdk.org/jdk/pull/28755/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28755&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372250
  Stats: 474 lines in 6 files changed: 173 ins; 287 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/28755.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28755/head:pull/28755

PR: https://git.openjdk.org/jdk/pull/28755