8212657: Implementation of JDK-8204089 Promptly Return Unused Committed Memory from G1 Summary: Issue optional, default enabled, concurrent cycles when the VM is idle to reclaim unused internal and Java heap memory. Reviewed-by: sjohanss, sangheki Contributed-by: Rodrigo Bruno <rbruno@gsd.inesc-id.pt>, Ruslan Synytsky <rs@jelastic.com>, Thomas Schatzl <thomas.schatzl@oracle.com>

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