RFR: 8322568: JFR: Improve metadata for IEEE rounding mode fields

[Erik Gahlin]

Could I have review of a couple of changes that align the style of the new event fields with other events, no abbreviations (env) and headline-style capitalization for the label.

Testring: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/19560/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19560&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322568
  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/19560.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19560/head:pull/19560

PR: https://git.openjdk.org/jdk/pull/19560