Add missing `public` modifier to Kotlin generated code

src/google/protobuf/compiler/java/enum_field.cc

@@ -287,7 +287,7 @@ void ImmutableEnumFieldGenerator::GenerateKotlinDslMembers(
   if (SupportUnknownEnumValue(descriptor_->file())) {
     printer->Print(
         variables_,
-        "$kt_deprecation$ var $kt_name$Value: kotlin.Int\n"
+        "$kt_deprecation$public var $kt_name$Value: kotlin.Int\n"
         "  @JvmName(\"${$get$kt_capitalized_name$Value$}$\")\n"
         "  get() = $kt_dsl_builder$.${$get$capitalized_name$Value$}$()\n"
         "  @JvmName(\"${$set$kt_capitalized_name$Value$}$\")\n"

src/google/protobuf/compiler/java/enum_field_lite.cc

@@ -329,7 +329,7 @@ void ImmutableEnumFieldLiteGenerator::GenerateKotlinDslMembers(
   if (SupportUnknownEnumValue(descriptor_->file())) {
     printer->Print(
         variables_,
-        "$kt_deprecation$ var $kt_name$Value: kotlin.Int\n"
+        "$kt_deprecation$public var $kt_name$Value: kotlin.Int\n"
         "  @JvmName(\"${$get$kt_capitalized_name$Value$}$\")\n"
         "  get() = $kt_dsl_builder$.${$get$capitalized_name$Value$}$()\n"
         "  @JvmName(\"${$set$kt_capitalized_name$Value$}$\")\n"

src/google/protobuf/compiler/java/message.cc

@@ -1525,7 +1525,7 @@ void ImmutableMessageGenerator::GenerateKotlinOrNull(io::Printer* printer) const
     const FieldDescriptor* field = descriptor_->field(i);
     if (field->has_presence() && GetJavaType(field) == JAVATYPE_MESSAGE) {
       printer->Print(
-          "val $full_classname$OrBuilder.$camelcase_name$OrNull: $full_name$?\n"
+          "public val $full_classname$OrBuilder.$camelcase_name$OrNull: $full_name$?\n"
           "  get() = if (has$name$()) get$name$() else null\n\n",
           "full_classname",
           EscapeKotlinKeywords(name_resolver_->GetClassName(descriptor_, true)),

src/google/protobuf/compiler/java/message_lite.cc

@@ -870,7 +870,7 @@ void ImmutableMessageLiteGenerator::GenerateKotlinOrNull(io::Printer* printer) c
     const FieldDescriptor* field = descriptor_->field(i);
     if (field->has_presence() && GetJavaType(field) == JAVATYPE_MESSAGE) {
       printer->Print(
-          "val $full_classname$OrBuilder.$camelcase_name$OrNull: "
+          "public val $full_classname$OrBuilder.$camelcase_name$OrNull: "
           "$full_name$?\n"
           "  get() = if (has$name$()) get$name$() else null\n\n",
           "full_classname",