RFR: 8253762: JFR: getField(String) should be able to access subfields

[Erik Gahlin]

Allow EventType::getFiled(String) to access subfields, similar to getValue(String) for values.

Testing: jdk/jdk/jfr

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Commit messages:
 - Remove trailing spaces
 - Initial

Changes: https://git.openjdk.java.net/jdk/pull/1606/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1606&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253762
  Stats: 39 lines in 4 files changed: 36 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1606.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1606/head:pull/1606

PR: https://git.openjdk.java.net/jdk/pull/1606