RFR: Use soft max capacity only for trigger calculations [v2]

[William Kemper]

> Use the soft max heap capacity only for the trigger's availability calculations. Our current generation sizing calculations cannot tolerate arbitrary changes to capacity. This use of soft max heap is consistent with original non-generational behavior. Here, the soft max heap capacity is applied directly as the heuristics view of the capacity of the young generation.

William Kemper has updated the pull request incrementally with two additional commits since the last revision:

 - Add comment for new method
 - Re-problem list test with intermittent failures

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Changes:
  - all: https://git.openjdk.org/shenandoah/pull/280/files
  - new: https://git.openjdk.org/shenandoah/pull/280/files/6eb01c0f..5b406484

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=280&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=280&range=00-01

  Stats: 5 lines in 2 files changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/shenandoah/pull/280.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/280/head:pull/280

PR: https://git.openjdk.org/shenandoah/pull/280