Add helper type aliases to type classes

I wonder why the standard library does not provide helpers for type classes.
Following a PR to add helpers for IsIterable for scala 2.x :

I would like to discuss if it would be worth to add such helpers in scala 3?
What are the reasons this was not done so far in scala 2?

IMO they ease the creation of instances and as you can see in the PR would also simplify code in the std-lib