RFR: 8310335 JFR: Modernize collections and switch statements

[Erik Gahlin]

Could I have a review of an update to the jfr modules to use more recent APIs and language constructs.

Testing: test/jdk/jdk/jfr

Thanks
Erik

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

Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/14547/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14547&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310335
  Stats: 256 lines in 92 files changed: 0 ins; 25 del; 231 mod
  Patch: https://git.openjdk.org/jdk/pull/14547.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14547/head:pull/14547

PR: https://git.openjdk.org/jdk/pull/14547