[css-align-4] (flex-)end fallback alignment for space-between

[LeaVerou]

Currently the fallback alignment for 1 item and space-between is start / flex-start.

I think flex-end / end makes just as much sense, and I recently ran into a use case that required exactly that. It would be good to have a way to control which way the fallback alignment goes. Perhaps as a second keyword in the alignment properties? E.g. justify-content: space-between flex-end;?

[fantasai]

We have resolutions on the syntax for this hanging around somewhere, just need to add it to L4!