In "Move task to..." workflow, separate visible and hidden columns in the dropdown

Summary:
Ref T13368. Currently, both visible and hidden columns are shown in the "Move tasks to..." dropdown on workflows from workboards.

When the dropdown contains hidden columns, move them to a separate section to make it clear that they're not likely targets.

Test Plan:
  - Used "Move tasks to project..." targeting a board with no hidden columns. Saw a single ungrouped dropdown.
  - Used "Move tasks to project..." targeting a board with hidden columns. Saw a dropdown grouped into "Visible" and "Hidden" columns.

Maniphest Tasks: T13368

Differential Revision: https://secure.phabricator.com/D20700

src/applications/project/controller/PhabricatorProjectColumnBulkMoveController.php

@@ -219,12 +219,40 @@ final class PhabricatorProjectColumnBulkMoveController
             ->setValue($dst_project->getDisplayName()));
       }
 
+      $column_options = array(
+        'visible' => array(),
+        'hidden' => array(),
+      );
+
+      $any_hidden = false;
+      foreach ($dst_columns as $column) {
+        if (!$column->isHidden()) {
+          $group = 'visible';
+        } else {
+          $group = 'hidden';
+        }
+
+        $phid = $column->getPHID();
+        $display_name = $column->getDisplayName();
+
+        $column_options[$group][$phid] = $display_name;
+      }
+
+      if ($column_options['hidden']) {
+        $column_options = array(
+          pht('Visible Columns') => $column_options['visible'],
+          pht('Hidden Columns') => $column_options['hidden'],
+        );
+      } else {
+        $column_options = $column_options['visible'];
+      }
+
       $form->appendControl(
         id(new AphrontFormSelectControl())
           ->setName('dstColumnPHID')
           ->setLabel(pht('Move to Column'))
           ->setValue($dst_column_phid)
-            ->setOptions(mpull($dst_columns, 'getDisplayName', 'getPHID')));
+          ->setOptions($column_options));
 
       $submit = pht('Move Tasks');