Card pre-cleaning.

We now pre-clean cards before the pause in the concurrent mark sweep
collectors. This provides substantial a pause time reduction for GC
iterations which have a lot of dirty cards. The only downside is a
slight GC time increase for large heaps.

Benchmark FormulaEvaluationActions.EvaluateAndApplyChanges:

Before:
Partial average pause: 5.47ms
Sticky average pause: 2.91ms
Total GC time: 25.8s

After:
Partial average pause: 1.98ms
Sticky average pause: 1.66ms
Total GC time: 27.0s

Benchmark score difference in the noise.

Change-Id: If9f01f8c1501f122e19432438108d48e723b332e