RFR: 8371985: Parallel: Move should_attempt_scavenge to ParallelScavengeHeap

[Albert Mingkun Yang]

Move young/full-gc criteria heuristics outside of `psScavenge.cpp` so that young-gc API runs to completion.

Test: tier1-3

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

Commit messages:
 - pgc-move-heuristic

Changes: https://git.openjdk.org/jdk/pull/28346/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28346&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371985
  Stats: 121 lines in 4 files changed: 53 ins; 62 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/28346.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28346/head:pull/28346

PR: https://git.openjdk.org/jdk/pull/28346