RFR: JDK-8305507 Add support for grace period before AbortVMOnSafepointTimeout triggers

[Wojciech Kudla]

As described https://bugs.openjdk.org/browse/JDK-8305507 this change adds a grace period before AbortVMOnSafepointTimeout activates to allow for JVM warm-up to conclude

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Commit messages:
 - JDK-8305507 Add support for grace period before AbortVMOnSafepointTimeout triggers

Changes: https://git.openjdk.org/jdk/pull/13386/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13386&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305507
  Stats: 6 lines in 2 files changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13386.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13386/head:pull/13386

PR: https://git.openjdk.org/jdk/pull/13386