Protobuf v6 support

[Tradias]

Some functions now return absl::string_view instead of const std::string& which seems to cause a compilation error in steamnetworkingsockets_internal.h:674. String_view has no c_str member function. See potential patch:

diff --git a/src/steamnetworkingsockets/steamnetworkingsockets_internal.h b/src/steamnetworkingsockets/steamnetworkingsockets_internal.h
index d5b0a97..ecaa53d 100644
--- a/src/steamnetworkingsockets/steamnetworkingsockets_internal.h
+++ b/src/steamnetworkingsockets/steamnetworkingsockets_internal.h
@@ -674,7 +674,7 @@ extern bool BSteamNetworkingIdentityToProtobufInternal( const SteamNetworkingIde
 #define SteamNetworkingIdentityToProtobuf( identity, msg, field_identity_string, field_identity_legacy_binary, field_legacy_steam_id ) \
 	{ SteamDatagramErrMsg identityToProtobufErrMsg; \
 		if ( !BSteamNetworkingIdentityToProtobuf( identity, msg, field_identity_string, field_identity_legacy_binary, field_legacy_steam_id, identityToProtobufErrMsg ) ) { \
-			AssertMsg2( false, "Failed to serialize identity to %s message.  %s", msg.GetTypeName().c_str(), identityToProtobufErrMsg ); \
+			AssertMsg2( false, "Failed to serialize identity to %s message.  %s", std::string(msg.GetTypeName()).c_str(), identityToProtobufErrMsg ); \
 		} \
 	}
 

Protobuf migration guide: https://protobuf.dev/support/migration/