a11y: Set project workboard button tooltips as aria-label

Summary:
Dropdown elements should have associated labels per https://www.w3.org/WAI/tutorials/forms/labels/
Setting the JS tooltips for the "Manage" and "Fullscreen" dropdowns also as their `aria-label` is clearly more accessible than exposing no hints at all.

Regarding the implemention,
* `$action->getName()` would return null as no name is set to be rendered in the UI next to the icon.
* introducing `$action->getTooltip()` in `PHUIListItemView` would also return null as this tooltip is created via JavaScript in `PhabricatorProjectBoardViewController` via `PHUIListItemView()->setMetadata()`. Thus do the ugly dance by parsing that very metadata for the sake of more accessibility on project workboards.

Ref T16072

Test Plan: Go to a project workboard, inspect the HTML of the two buttons in the upper right corner for "Manage" and "Fullscreen", see an `aria-label` in the HTML code, have happier screenreader users who appreciate links which have a discernible name.

Reviewers: O1 Blessed Committers, chris

Reviewed By: O1 Blessed Committers, chris

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T16072

Differential Revision: https://we.phorge.it/D26050

src/view/phui/PHUICrumbsView.php

···
           $action_classes[] = 'phui-crumbs-action-disabled';
         }
 
+        $aria_label = null;
+        $metadata = $action->getMetadata();
+        if ($metadata && isset($metadata['tip'])) {
+          $aria_label = $metadata['tip'];
+        }
+
         $actions[] = javelin_tag(
           'a',
           array(
             'href' => $action->getHref(),
             'class' => implode(' ', $action_classes),
             'sigil' => implode(' ', $action_sigils),
+            'aria-label' => $aria_label,
             'style' => $action->getStyle(),
             'meta' => $action->getMetadata(),
           ),