message attributes not retrieved

[MikeOfZen]

Message attributes are not accessible via l10n.format_value("message.attribute") - the method returns "message.attribute" instead of the expected attribute value.

sample ftl

 test-button = 
     .value = Click Me
     .title = This is a test button
     .aria-label = Test button for accessibility

l10n.format_value("test-button.value") should return "Click Me" but instead just returns "test-button.value"

looking at bundle has_message and get_message, the search is by msg_id, but the attributes are stored in attributes of a message without a way of retrieveing them.