Overdue Shadow Catcher features

I experienced a few issues with the Shadow Catcher and a quick google search made me realize just how broken it is.

devtalk.blender.org/t/lets-finally-fix-the-shadowcatcher/691

Apparently it's been a problem for a couple years and even though it's an essential tool for VFX it didn't get fixed. I understand implementing it in Eeve is not a priority since it's rarely used for photorealism but please let's try to fix it in Cycles.