Describe the feature

The requested shapes and similar ones can be achieved in the upcoming 1.20.6 release with the various double stair blocks (Double Stairs, Divided Stairs, Sliced Stairs and their vertical equivalents). Backporting these to 1.20.1 is unfortunately not possible.

I'm not totally sure about this one, it seems kinda niche to me. I'll think about it.

the reason i want them is because there's no cornerblock for sliced stairs

Ok, yeah, that sounds reasonable. I'll add it to my list

also these two for the same reason

I will most likely do those two differently, see #409 for more details.