Let players change the direction a formation is facing

This is basically an extension to the existing movement command. Right now, formations in AoE2 will always face in the direction the units are coming from. This makes the direction of a formation unpredictable as players never know the exact path a group will take.

How does it work?

RIGHT-CLICK followed by an immediate release of the moue button will work as before. The direction of a formation would be changed by holding RIGHT-CLICK and dragging the mouse pointer in the direction the formation should face (see below).

Moving the mouse pointer will pivot the formation around the point where the player right-clicked. Unit lines will always be orthogonal to the line between pivot point and mouse pointer. To aid the player in choosing the right direction, the UI should display the selection circles where the units will stand when arrivng.

Will this change the balance?

Unlikely, since right-clicking without drag will always be faster. I see the main use case for unit groups that are moved long distances across the map, where the direction of a formation is generally unpredictable. Just in case, we should give players the option to turn this feature off in MP games. Then it remains a nice addition to single player.

No files, tests, or entry points are named. Start by locating the existing movement command and formation input and rendering code; the work is done when dragging after a right-click previews and applies the formation direction, while an immediate release preserves current behavior and multiplayer can disable the feature.