Add SetNonNullable alternative names

[igas]

I was migrating from other library and was looking for recursive NonNullable, which was called DeepNonNullable. Only through search in issues I found SetNonNullable.

Related #795

[som-sm]

SetNonNullable doesn't work for deeply nested key.

type T = SetNonNullable<{a: {b: string | null}}>;
//   ^? type T = {
//          a: {
//              b: string | null;
//          };
//      }