[FR] Consider a "no toggling" modifier for the wait command

If you've got a waiting unit and a non-waiting unit selected and give the Wait command, both will toggle their state so you still have one of each. Consider supporting a modifier (CTRL or something) that makes the command only affect those who aren't yet waiting, such that the result after the command is that everybody is waiting, unless that was already the state in which case it unwaits everybody.

The request isn't that important because it can be Lua'd without that much trouble, but I think it makes sense to have sensible behaviour in the engine.

Start by locating the Wait command handling and how command modifiers are represented in the engine. Check how selected waiting and non-waiting units currently respond, then define completion as a modifier that makes all selected units wait, or unwaits all of them when they are already waiting; add or update relevant tests if the command has coverage.

Written by the indexing model from the issue text.