Option for 'Transform dashes in URL to spaces in term name filter values' on term arguments doesn't affect the query

The term name argument validator has an option to convert dashes to spaces in the argument value, which means that you can have a URL like 'myview/term-name-with-spaces'.

The argument validator handles this correctly, but the query that is run with this by the term name argument is incorrect. With a simple view of article nodes and the tags field that comes OOTB with core, I get this clause in the query:

WHERE (( (taxonomy_term_field_data_node__field_tags.name = 'has-spaces') )AND(( (node_field_data.status = '1') )))
ORDER BY node_field_data_created DESC

Argument validator plugins only return a boolean from validateArgument(), but on D7 the equivalent function views_plugin_argument_validate_taxonomy_term::validate_argument() doctored the argument value on the argument handler like this:

        if ($term && (empty($vocabularies) || !empty($vocabularies[$term->machine_name]))) {
          if ($type == 'convert') {
            $this->argument->argument = $term->tid;
          }

There doesn't seem to be any provision for this in D8 -- argument validator plugins don't seem to be able to influence the argument value that the rest of the view uses.