JFR: getField(String) should be able to access nested fields

Summary

Clarify that RecordedObject::hasField(String) can access nested fields and add support for nested field access to EventType::getField(String).

Problem

JDK Flight Recorder can emit events with composite/struct values, for example methods and classes. To index into a nested value it is possible to use a ".", for example RecordedEvent::getValue("allocatedClass.name").

It is however not possible to access metadata about a value the same way, for example RecordedObject::hasField("allocatedClass.name") or EventType::getField("allocationClass.name"). This is inconvenient if you want to check if a field exist before you call getValue(String), or if you want to access metadata about a value, for example the unit.

Solution

The solution is to update the specification for RecordedObject:hasField(String) so it says that it is possible to use nested access, the implementation already supports it.

Also add support for nested field access for EventType::getField(String) and update the specification accordingly.

Specification

jdk.jfr.RecordedObject

 /**
   * Returns {@code true} if a field with the given name exists,  {@code false} otherwise.
+  * <p>
+  * It's possible to index into a nested field by using {@code "."} (for
+  * instance {@code "thread.group.parent.name}").
   *
   * @param name name of the field to get, not {@code null}
   *
   * @return {@code true} if the field exists, {@code false} otherwise
   *
   * @see #getFields()
   */
  public boolean hasField(String name) {

jdk.jfr.EventType

 /**
   * Returns the field with the specified name, or {@code null} if it doesn't
   * exist.
+  * <p>
+  * It's possible to index into a nested field by using {@code "."} (for
+  * instance {@code "thread.group.parent.name}").
   *
   * @param name of the field to get, not {@code null}
   *
  * @return a value descriptor that describes the field, or {@code null} if
  *         the field with the specified name doesn't exist
  */
 public ValueDescriptor getField(String name) {