Improve Dark Mode for result type icons in Typeahead results
Summary:
`.phui-font-fa` generically defines `color: {$darkgreytext}` for icons, while `.phabricator-main-search-typeahead-result .result-type` defines `color: {$lightgreytext}`.
This already results in a color mismatch visible in Default Mode but even more so in Dark Mode.
Thus explicitly set also `color: {$lightgreytext}` for the corresponding icon via `.phabricator-main-search-typeahead-result .result-type .phui-font-fa`.
Refs T15056
Test Plan:
* Go to http://phorge.localhost/settings/panel/display/ and set `Accessibility` to `Dark Mode (Experimental)`
* Go to a Maniphest task, select Edit Task, click the Magnifier icon in the Subscribers field, click the Magnifier icon in the Projects field.
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T15056
Differential Revision: https://we.phorge.it/D26392