RFR: 8366781: Parallel: Include OS free memory in GC selection heuristics [v4]

[Albert Mingkun Yang]

> Add a new condition checking if OS has enough free memory to commit/expand old-gen, which determines whether the upcoming GC should be young or full.
> 
> This is needed only when `UseAdaptiveSizePolicy` is on, because this is intended to avoid including extra OS-time in gc-pause-time tracking, used for young-gen resizing.
> 
> Test: tier1-3

Albert Mingkun Yang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains eight additional commits since the last revision:

 - Merge branch 'master' into pgc-os-free-mem
 - review
 - sizet
 - Merge branch 'master' into pgc-os-free-mem
 - Merge branch 'master' into pgc-os-free-mem
 - review
 - Merge branch 'master' into pgc-os-free-mem
 - pgc-os-free-mem

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27068/files
  - new: https://git.openjdk.org/jdk/pull/27068/files/2267e5c0..affa0435

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27068&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27068&range=02-03

  Stats: 26018 lines in 655 files changed: 15588 ins; 7978 del; 2452 mod
  Patch: https://git.openjdk.org/jdk/pull/27068.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27068/head:pull/27068

PR: https://git.openjdk.org/jdk/pull/27068