RFR: 8366781: Parallel: Include OS free memory in GC selection heuristics [v5]

[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 10 additional commits since the last revision:

 - review
 - Merge branch 'master' into pgc-os-free-mem
 - 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/affa0435..47bf31ad

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27068&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27068&range=03-04

  Stats: 5184 lines in 151 files changed: 3020 ins; 1057 del; 1107 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