Masking and clipping not working

[dirkschulze]

Generator does not support VectorMasks or any other mask yet.

Also see

adobe-photoshop/generator-core#234

[dirkschulze]

@chrisbank noted that we might have all information for Vector masks and maybe raster masks to implement it in SVG. We'll need to check that.

[imaderyc]

watson bug
vector mask: https://watsonexp.corp.adobe.com/#bug=3853040 (we heard complains from at least 1 user about masks not working in SVG, so would be good to fix for Crema)
clipping mask: https://watsonexp.corp.adobe.com/#bug=3833741