RFR: 7201: JdkAttributes.OS_SWITCH_RATE does not work consistently across JFRs from different JDK versions.

[Suchita Chaturvedi]

This PR addresses the issue of switchRate attribute not accessible via core API when used for JFR generated with JDK 11 and above.

Please review the change and provide your valuable comments.

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Commit messages:
 - JdkAttributes.OS_SWITCH_RATE does not work consistently across JFRs from different JDK versions.

Changes: https://git.openjdk.java.net/jmc/pull/246/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=246&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7201
  Stats: 17 lines in 4 files changed: 15 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jmc/pull/246.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/246/head:pull/246

PR: https://git.openjdk.java.net/jmc/pull/246