Add volatile to featuresResolved (#20767)

PiperOrigin-RevId: 738832869

Author: zhangskz

java/core/src/main/java/com/google/protobuf/Descriptors.java

@@ -537,7 +537,7 @@ public interface InternalDescriptorAssigner {
     private final FileDescriptor[] dependencies;
     private final FileDescriptor[] publicDependencies;
     private final DescriptorPool pool;
-    private boolean featuresResolved;
+    private volatile boolean featuresResolved;
 
     private FileDescriptor(
         final FileDescriptorProto proto,