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