Make JfrClass field method public so that G1HeapSummary class has access to determine difference in fields based on jdk version. (#971)

src/converter/one/jfr/JfrClass.java

@@ -9,7 +9,7 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 
-class JfrClass extends Element {
+public class JfrClass extends Element {
     final int id;
     final boolean simpleType;
     final String name;
@@ -29,7 +29,7 @@ class JfrClass extends Element {
         }
     }
 
-    JfrField field(String name) {
+    public JfrField field(String name) {
         for (JfrField field : fields) {
             if (field.name.equals(name)) {
                 return field;

src/converter/one/jfr/JfrField.java

@@ -7,7 +7,7 @@ package one.jfr;
 
 import java.util.Map;
 
-class JfrField extends Element {
+public class JfrField extends Element {
     final String name;
     final int type;
     final boolean constantPool;