swap the meaning of alt and shift in the undo commands

since **alt** is used to _reverse_ the direction of the motion in commands like `f` and `t`, and **shift** is used to deal with _extend (basicly selection)_ like in all other commands can we swap `<a-u>` with `U` so that **alt** for _redo instead of undo_ and **shift** for _selection history rather than change history_ I would like hiding that change behind an option to give people time to adapt to it, and a few versions afterward make the default of kakoune to use <a-u> for redo and U for undo selection. and so u stays the same and <a-U> does the same thing (alt for redo the last edit, shift for selection rather than edits)