Breaking change: Lock down visibility for descriptor syntax APIs.

Users should migrate to corresponding feature accessors (e.g. FieldDescriptor.hasPresence, EnumDescriptor.isClosed) instead of deriving these based on syntax, which will break after under Editions (https://protobuf.dev/editions/overview/)

PiperOrigin-RevId: 586518687

Author: zhangskz

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

@@ -140,8 +140,6 @@ public List<FileDescriptor> getPublicDependencies() {
     }
 
     /** The syntax of the .proto file. */
-    @Deprecated
-    public
     enum Syntax {
       UNKNOWN("unknown"),
       PROTO2("proto2"),
@@ -156,8 +154,6 @@ enum Syntax {
     }
 
     /** Get the syntax of the .proto file. */
-    @Deprecated
-    public
     Syntax getSyntax() {
       if (Syntax.PROTO3.name.equals(proto.getSyntax())) {
         return Syntax.PROTO3;
@@ -1273,8 +1269,6 @@ public OneofDescriptor getRealContainingOneof() {
      * Returns true if this field was syntactically written with "optional" in the .proto file.
      * Excludes singular proto3 fields that do not have a label.
      */
-    @Deprecated
-    public
     boolean hasOptionalKeyword() {
       return isProto3Optional
           || (file.getSyntax() == Syntax.PROTO2 && isOptional() && getContainingOneof() == null);
@@ -2843,8 +2837,6 @@ public OneofDescriptorProto toProto() {
       return proto;
     }
 
-    @Deprecated
-    public
     boolean isSynthetic() {
       return fields.length == 1 && fields[0].isProto3Optional;
     }

ruby/src/main/java/com/google/protobuf/jruby/RubyMessage.java

@@ -42,6 +42,7 @@
 import com.google.protobuf.DynamicMessage;
 import com.google.protobuf.InvalidProtocolBufferException;
 import com.google.protobuf.LegacyDescriptorsUtil.LegacyFileDescriptor;
+import com.google.protobuf.LegacyDescriptorsUtil.LegacyOneofDescriptor;
 import com.google.protobuf.Message;
 import com.google.protobuf.UnknownFieldSet;
 import com.google.protobuf.util.JsonFormat;
@@ -1340,7 +1341,7 @@ private IRubyObject setFieldInternal(
         // Keep track of what Oneofs are set
         if (value.isNil()) {
           oneofCases.remove(oneofDescriptor);
-          if (!oneofDescriptor.isSynthetic()) {
+          if (!LegacyOneofDescriptor.isSynthetic(oneofDescriptor)) {
             addValue = false;
           }
         } else {