Make autocomplete text invisible in search bar

[hackartisan]

Set the opacity to 0. See this blacklight commit for guidance: https://github.com/projectblacklight/blacklight/pull/2807/files

child of #1165

[hackartisan]

The CSS ways of doing this had undesirable accessibility side effects. Either we could hide the autocompleted text visually but not from screen readers, or we could effectively hide it but it also hid the search bar from screen readers.

It looks like there's a hint option on the typeahead initialization that is set to "true" in blacklight. It seems worth trying to override that initialization and set it to false instead.

https://github.com/twitter/typeahead.js/blob/master/doc/jquery_typeahead.md

I would try copying most of https://github.com/projectblacklight/blacklight/blob/v7.29.0/app/javascript/blacklight/autocomplete.js into pulfalight_loader.es6 to see if we can initialize it with the hint off.

Also, an interesting note, blacklight has removed twitter typeahead for version 8: projectblacklight/blacklight#2576