Add the option to preview all mask blending effects

[wzk20010221]

Pre-Flight checklist

• [x] Did you check to see if this issue already exists?
• [x] This is a single feature request. (Do not put multiple feature requests in one issue)

Describe The Feature Request Below

Now I can preview the selected mask of the selected layer. However, when creating a texture, multiple masks are usually used for blending, such as Multiply or Subtract. But currently, there is no way to preview the effect of blending multiple masks together. Only the selected mask can be viewed, and the overall mask of the layer cannot be viewed.

[wzk20010221]

This Function is Very important Like paint in Adobe painter

[ucupumar]

Masks are actually part of the layer's alpha, so you can preview that entirely if you choose Alpha option beside the preview mode.