message: Add a better error message for UnsupportedColumnTypeException on subtables
diff: @@ -764,10 +764,18 @@ Results::OutOfBoundsIndexException::OutOfBoundsIndexException(size_t r, size_t c
  : std::out_of_range(util::format("Requested index %1 greater than max %2", r, c - 1))
  , requested(r), valid_count(c) {}
  +static std::string unsupported_operation_msg(size_t column, const Table* table, const char* operation)
  +{
  + const char* column_type = string_for_property_type(ObjectSchema::from_core_type(*table->get_descriptor(), column));
  + if (table->is_group_level())
  + return util::format("Cannot %1 property '%2': operation not supported for '%3' properties",
  + operation, table->get_column_name(column), column_type);
  + return util::format("Cannot %1 '%2' array: operation not supported",
  + operation, column_type);
  +}
  +
  Results::UnsupportedColumnTypeException::UnsupportedColumnTypeException(size_t column, const Table* table, const char* operation)
  -: std::logic_error(util::format("Cannot %1 property '%2': operation not supported for '%3' properties",
  - operation, table->get_column_name(column),
  - string_for_property_type(ObjectSchema::from_core_type(*table->get_descriptor(), column))))
  +: std::logic_error(unsupported_operation_msg(column, table, operation))
  , column_index(column)
  , column_name(table->get_column_name(column))
  , property_type(ObjectSchema::from_core_type(*table->get_descriptor(), column))
  