[Docs] v5 migration guide doesn't mention removal of .rounded-sm/lg

[kylefox]

It looks like #31687 removed .rounded-sm and .rounded-lg and introduced .rounded-0-.rounded-3

This change totally makes sense, but I think maybe it's missing from the Migrating to v5 docs?

[k99sharma]

Hi this is my first time contributing. I tried to solve this issue can anyone check if its right.