RFR: 8247471: Enhance CPU load events with the actual elapsed CPU time

[Jaroslav Bachorik]

A continuation of an RFR thread started last year - https://mail.openjdk.java.net/pipermail/hotspot-jfr-dev/2020-June/001533.html

This change adds the raw CPU time value to CPU load events (per-thread and per-process as well). 
The CPU time value is already known and used to calculate the load so adding it to the events does not incur any extra overhead while making it much easier for the end users to eg. aggregate and compare the active execution time per time period without the detailed knowledge how JFR computes and normalizes the CPU load.

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Commit messages:
 - Fix wording and remove unnecessary debug output
 - Fix jcheck
 - Merge branch 'master' into 8247471_cpuload_with_time
 - 8247471: Enhance CPU load events with the actual elapsed CPU time

Changes: https://git.openjdk.java.net/jdk/pull/2186/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2186&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8247471
  Stats: 543 lines in 11 files changed: 238 ins; 205 del; 100 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2186.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2186/head:pull/2186

PR: https://git.openjdk.java.net/jdk/pull/2186