"Cancel" button on extended operations progress sheets

[Brad Brighton 62]

I've encountered cases now where the Inpainting Brush hangs (def: indicator stops progressing after approx. 80% represented completion). I haven't been able to repro this specific failure in the beta so I suppose it's fixed but I've also seen extended (minutes long, even in the beta) behaviors in other operations that display modal progress sheets (such as "Analyzing Scene" in prep for the haze removal filter).

The request is that for any of the operations that present the modal progress sheet, offer a cancel button on that sheet that will take the project back to the state prior to invoking whatever process is active.