[crac] RFR: 8348650: [CRaC] Limit heap size before checkpoint

[Timofei Pushkin]

Adds `CRaCMaxHeapSizeBeforeCheckpoint` to allow limiting heap size before checkpoint and adds its support into G1

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Commit messages:
 - Limit heap size before checkpoint

Changes: https://git.openjdk.org/crac/pull/189/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=189&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348650
  Stats: 205 lines in 10 files changed: 183 ins; 1 del; 21 mod
  Patch: https://git.openjdk.org/crac/pull/189.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/189/head:pull/189

PR: https://git.openjdk.org/crac/pull/189