Make closed objects in global typeahead look closed

Summary:
Fixes T6906.

I found the code in behavior-search-typeahead.js that was throwing away the closedness-detction work done in Prejab.js::transformDatasourceResults. Modified it to re-add the correct class name to the phabricator-main-search-typeahead-result elements.

Then I found some CSS in typeahead-browse.css and completely flailed around until realizing that particular CSS only gets loaded when hitting the typeahead endpoint directly. Copied the relevant bit of CSS over to main-menu-view.css (but maybe it should be removed from typeahead-browse.css?).

This is my first JS/CSS change, so please don't assume I did anything right.

Test Plan:

Reviewers: Blessed Reviewers, chad

Reviewed By: Blessed Reviewers, chad

Subscribers: epriestley

Maniphest Tasks: T6906

Differential Revision: https://secure.phabricator.com/D18017