RFR: 8318098: Update jfr tests to replace keyword jfr with vm.flagless

[Leonid Mesnik]

A lot of jfr tests are very specific. Currently all of them are marked with jfr keyword and excluded when VM flags are set.

It makes sense to mark them with @requires <something> to be complaint with all other openjdk tests. 
The next step is to review tests and remove vm.flagless from tests that should be executed with different VM flags.

Bug https://bugs.openjdk.org/browse/JDK-8318097 is filed for this activity.

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Commit messages:
 - 8318098: Update jfr tests to replace keyword jfr with vm.flagless

Changes: https://git.openjdk.org/jdk/pull/23285/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23285&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318098
  Stats: 1090 lines in 582 files changed: 2 ins; 0 del; 1088 mod
  Patch: https://git.openjdk.org/jdk/pull/23285.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23285/head:pull/23285

PR: https://git.openjdk.org/jdk/pull/23285