Mark `FieldDescriptor.hasOptionalKeyword()` as deprecated.

This API will be removed in a future breaking change.

PiperOrigin-RevId: 547505900

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

@@ -1266,7 +1266,9 @@ public final class Descriptors {
      * Returns true if this field was syntactically written with "optional" in the .proto file.
      * Excludes singular proto3 fields that do not have a label.
      */
-    public boolean hasOptionalKeyword() {
+    @Deprecated
+    public
+    boolean hasOptionalKeyword() {
       return isProto3Optional
           || (file.getSyntax() == Syntax.PROTO2 && isOptional() && getContainingOneof() == null);
     }

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

@@ -30,6 +30,7 @@
 
 package com.google.protobuf;
 
+import com.google.protobuf.Descriptors.FieldDescriptor;
 import com.google.protobuf.Descriptors.FileDescriptor;
 import com.google.protobuf.Descriptors.OneofDescriptor;
 
@@ -70,6 +71,16 @@ public final class LegacyDescriptorsUtil {
     private LegacyFileDescriptor() {}
   }
 
+  /** Wraps FieldDescriptor */
+  public static final class LegacyFieldDescriptor {
+
+    public static boolean hasOptionalKeyword(FieldDescriptor descriptor) {
+      return descriptor.hasOptionalKeyword();
+    }
+
+    private LegacyFieldDescriptor() {}
+  }
+
   /** Wraps OneofDescriptor */
   public static final class LegacyOneofDescriptor {