Make InnerClassInfo thread-safe

This change adjusts fields in InnerClassInfo to be volatile, if those
fields can cause concurrency problems. In particular, the following
methods result in issues when ran with Java 25 in a multi-threade
environment:

* getEnclosingTypeName
* getName
* getSourceName

They follow the pattern of checking whether some value is initialized
with a boolean variable, then setting the value if its not initialized
yet. When those methods are invoked from multiple threads on the same
object, there is no guarantee that the initialized value will be read by
all threads. By making both the flag and the value fields are volatile,
threads will read the correct value; the value could still be
initialized multiple times, but we assume that all threads will be
setting the same value.

This change additionally makes some fields final, to make the code
easier to read and analyze.

Fixes: eclipse-jdt#4199

Author: trancexpress

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/classfmt/ClassFileStruct.java

@@ -16,7 +16,7 @@
 abstract public class ClassFileStruct {
 	byte[] reference;
 	int[] constantPoolOffsets;
-	int structOffset;
+	final int structOffset;
 public ClassFileStruct(byte[] classFileBytes, int[] offsets, int offset) {
 	this.reference = classFileBytes;
 	this.constantPoolOffsets = offsets;

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/classfmt/InnerClassInfo.java

@@ -22,16 +22,16 @@
  */
 
 public class InnerClassInfo extends ClassFileStruct implements IBinaryNestedType {
-	int innerClassNameIndex = -1;
-	int outerClassNameIndex = -1;
-	int innerNameIndex = -1;
-	private char[] innerClassName;
-	private char[] outerClassName;
-	private char[] innerName;
-	private int accessFlags = -1;
-	private boolean readInnerClassName;
-	private boolean readOuterClassName;
-	private boolean readInnerName;
+	final int innerClassNameIndex;
+	final int outerClassNameIndex;
+	final int innerNameIndex;
+	private volatile char[] innerClassName;
+	private volatile char[] outerClassName;
+	private volatile char[] innerName;
+	private volatile int accessFlags = -1;
+	private volatile boolean readInnerClassName;
+	private volatile boolean readOuterClassName;
+	private volatile boolean readInnerName;
 
 public InnerClassInfo(byte classFileBytes[], int offsets[], int offset) {
 	super(classFileBytes, offsets, offset);