The Canon EF-S 10-22mm is a f/3.5-4.5 lens. Here is the size/weight; 3.3" x 3.5", 13.6 oz. / 83.5 x 89.8mm, 385g. It uses a 77mm filter. This is a BIG lens!
How much smaller will a 11-22mm f/4-5.6 IS STM be I doubt that the camera/lens combo will fit in a pocket.
Potentially quite a bit smaller. You aren't comparing apples to apples here. The EF-M format has a MUCH shorter flange focal distance vs. EF/EF-S (18mm vs. 44mm). This allows for alot of opportunity for space savings in the lens.
I'd expect it's physical size will be a good amount shorter then the EF-S 10-22.