RFR: Expand old on demand [v62]

[Kelvin Nilsen]

> This PR describes several proposed changes to dynamically adjust the sizes of old-gen and young-gen.  In general, the objective is to keep old-gen as small as possible so that there is an abundance of memory available for the young-gen allocation runway.
> 
> This PR now passes all GHA pre-integration tests and other internal CI tests.

Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:

  Keep lock while transferring regions to young
  
  In ShenandoahFreeSet::move_collector_sets_to_mutator(), we had released the lock before transferring
  OldCollector regions to young so that they could become part of the Mutator free set.  This commit
  fixes that error.

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

Changes:
  - all: https://git.openjdk.org/shenandoah/pull/248/files
  - new: https://git.openjdk.org/shenandoah/pull/248/files/92608d74..e02032d3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=248&range=61
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=248&range=60-61

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/shenandoah/pull/248.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/248/head:pull/248

PR: https://git.openjdk.org/shenandoah/pull/248