Unlink layer mask
Description of the feature
Ability to unlink a mask from its layer (group) so both can be moved independently. Might be enough to support it for layer groups, if that makes it easier.
Use cases
Right now I'm trying to have one layer (partially transparent) cast a drop shadow onto another (think one doughnut in front of another). But fine tuning the position is tedious because you must redo the drop shadow masking procedure. A drop shadow layer effect would fix this case, but the general problem is re-positioning things behind a layer mask without moving the mask itself.