RFR: JDK-8298255: JFR provide information about dynamization of number of compiler threads

[Matthias Baesken]

The JVM supports both dynamic GC threads, and dynamic Compiler threads.
While the GCConfiguration JFR event (see https://sap.github.io/SapMachine/jfrevents/#gcconfiguration ) seems to have at least some info about dynamization of GC threads ( field usesDynamicGCThreads), the JIT CompilerConfiguration event seems to miss this info (about JIT compiler threads dynamization), this should be added; currently the impression is given that the number is static but this is often not the case.
As an extension, the dynamization process of adding / removing threads could be added as well to the JFR events but I am not sure if this is desired so I just started with a very simple patch.

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Commit messages:
 - JDK-8298255

Changes: https://git.openjdk.org/jdk/pull/11563/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11563&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298255
  Stats: 4 lines in 3 files changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11563.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11563/head:pull/11563

PR: https://git.openjdk.org/jdk/pull/11563