RFR: 8281536: JFR: Improve jdk.jfr.ContentType documentation

[Erik Gahlin]

Hi,

Could I have a review of an enhancement that improves the documentation of the jdk.jfr.ContentType annotation.

Testing: tier1 + /test/jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.java.net/jdk/pull/7403/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7403&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281536
  Stats: 98 lines in 2 files changed: 98 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7403.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7403/head:pull/7403

PR: https://git.openjdk.java.net/jdk/pull/7403