GH-45807: [C++] introduce compatiblity with protobuf 30

This version of protobuf has switched a few interface types from
`std::string` to `std::string_view` and therefore introcuces some
breaking changes in the code. Fix these by applying appropriate casts.

Link: https://protobuf.dev/support/migration/#v30
Signed-off-by: Christian Heusel <christian@heusel.eu>

Author: christian-heusel

cpp/src/arrow/engine/substrait/expression_internal.cc

@@ -142,7 +142,7 @@ std::string EnumToString(int value, const google::protobuf::EnumDescriptor* desc
   if (value_desc == nullptr) {
     return "unknown";
   }
-  return value_desc->name();
+  return std::string(value_desc->name());
 }
 
 Result<compute::Expression> FromProto(const substrait::Expression::ReferenceSegment* ref,

cpp/src/arrow/engine/substrait/serde.cc

@@ -62,8 +62,8 @@ Status ParseFromBufferImpl(const Buffer& buf, const std::string& full_name,
 template <typename Message>
 Result<Message> ParseFromBuffer(const Buffer& buf) {
   Message message;
-  ARROW_RETURN_NOT_OK(
-      ParseFromBufferImpl(buf, Message::descriptor()->full_name(), &message));
+  ARROW_RETURN_NOT_OK(ParseFromBufferImpl(
+        buf, std::string(Message::descriptor()->full_name()), &message));
   return message;
 }
 

cpp/src/arrow/engine/substrait/util_internal.cc

@@ -30,7 +30,7 @@ std::string EnumToString(int value, const google::protobuf::EnumDescriptor& desc
   if (value_desc == nullptr) {
     return "unknown";
   }
-  return value_desc->name();
+  return std::string(value_desc->name());
 }
 
 std::unique_ptr<substrait::Version> CreateVersion() {