RFR: JDK-8305506: Add support for fractional values of SafepointTimeoutDelay [v3]

[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:

  Removed dedicated format declaration for jdouble, added test case for floating point type of -XX:SafepointTimeoutDelay

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13373/files
  - new: https://git.openjdk.org/jdk/pull/13373/files/a8fdc733..7c49b4d7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13373&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13373&range=01-02

  Stats: 16 lines in 3 files changed: 6 ins; 3 del; 7 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