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

[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.

Test: tier1-3

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Commit messages:
 - pgc-os-free-mem

Changes: https://git.openjdk.org/jdk/pull/27068/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27068&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366781
  Stats: 31 lines in 1 file changed: 20 ins; 0 del; 11 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