RFR: 8369692: JFR: Don't record thread metadata in case jdk.ThreadStart is disabled

[Kerem Kat]

### Before
File size: 0.84 MB
Scrubbed size: 0.82 MB
Waste: 2.73%

### After
File size: 0.80 MB
Scrubbed size: 0.78 MB
Waste: 3.40%

File size decreases when `ThreadStart` and `ThreadEnd` events are disabled.

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Commit messages:
 - 8369692: JFR: Don't record thread metadata in case jdk.ThreadStart is disabled

Changes: https://git.openjdk.org/jdk/pull/28222/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28222&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369692
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/28222.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28222/head:pull/28222

PR: https://git.openjdk.org/jdk/pull/28222