RFR: 8352185: Shenandoah: Invalid logic for remembered set verification

[Xiaolong Peng]

There are some scenarios in which GenShen may have improper remembered set verification logic:

1. Concurrent young cycles following a Full GC:

In the end of ShenandoahFullGC, it resets bitmaps for the entire heap w/o resetting marking context to be incomplete, but ShenandoahVerifier has code like below to get a complete old marking context for remembered set verification


ShenandoahVerifier  
ShenandoahMarkingContext* ShenandoahVerifier::get_marking_context_for_old() {
  shenandoah_assert_generations_reconciled();
  if (_heap->old_generation()->is_mark_complete() || _heap->gc_generation()->is_global()) {
    return _heap->complete_marking_context();
  }
  return nullptr;
}


For the concurrent young GC cycles after a full GC, the old marking context used for remembered set verification is stale, and may cause unexpected result. 

2. For the impl of `ShenandoahVerifier::get_marking_context_for_old` mentioned above, it always return a marking context for global GC, but marking bitmaps is already reset before before init-mark, `ShenandoahVerifier::help_verify_region_rem_set` always skip verification in this case. 

3. ShenandoahConcurrentGC always clean remembered set read table, but only swap read/write table when gc generation is young, this issue causes remembered set verification before init-mark to use a completely clean remembered set, but it is covered by issue 2. 


### Test
- [x] `make test TEST=hotspot_gc_shenandoah`

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

Commit messages:
 - Clean and rebuild rem-set in global gc
 - Set mark incomplete after ShenandoahMCResetCompleteBitmapTask
 - Only clean rem-set read table in young gc; not verify rem-set in concurrent global GC in generational mode
 - Always swap card table in generational mode so the table can be properly rebuilt through marking.
 - Initial works

Changes: https://git.openjdk.org/jdk/pull/24092/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24092&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8352185
  Stats: 42 lines in 4 files changed: 17 ins; 16 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/24092.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24092/head:pull/24092

PR: https://git.openjdk.org/jdk/pull/24092