RFR: Handle old, pinned regions [v6]

[William Kemper]

> Prior to this change, mixed collections were entirely ignoring the pinned status of old regions. Pinned old regions would not be coalesced and filled (which could lead to a crash) and their pin status was not being synchronized with the pin count (which could also lead to a crash). To address these problems, the following changes have been made:
> 
> * Before adding old regions to the collection set, their pinned status is synchronized.
> * Pinned old regions will _not_ be added to a mixed collection, they will be skipped and considered for inclusion in the next mixed collection.
> * Any old regions which have not been evacuated after the last mixed collection will be made parseable (coalesced and filled) _at the start of the next old marking cycle_.

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Do not drop abbreviated argument when recording success concurrent cycle

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Changes:
  - all: https://git.openjdk.org/shenandoah/pull/149/files
  - new: https://git.openjdk.org/shenandoah/pull/149/files/9f569892..73fd90e8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=149&range=05
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=149&range=04-05

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah/pull/149.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah pull/149/head:pull/149

PR: https://git.openjdk.org/shenandoah/pull/149