RFR: JDK-8305506: Add support for fractional values of SafepointTimeoutDelay [v5]

[Wojciech Kudla]

> As stated in https://bugs.openjdk.org/browse/JDK-8305506 this change replaces SafepointTimeoutDelay as integer value with a floating point type to support sub-millisecond SafepointTimeout thresholds.
> This is immensely useful for investigating time-to-safepoint issues in low latency space.

Wojciech Kudla has updated the pull request incrementally with one additional commit since the last revision:

  Adjusted test case to verify integer value

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13373/files
  - new: https://git.openjdk.org/jdk/pull/13373/files/3b22f3a2..e4cb3b91

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13373&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13373&range=03-04

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13373.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13373/head:pull/13373

PR: https://git.openjdk.org/jdk/pull/13373