[v3] Make behavior of Join on Nothing less surprising

[Yash Thakur]

The behavior of Join on Nothing is a bit surprising on lists. I would've expected something like ["foo", [4, 2], 3] to be turned either into "foo[4,2]3" or "foo423" or even ["foo", "42", "3"], rather than ["", "42", [[1, 1, 1], [1, 2], [3]]]. On strings, it's basically useless, which is not great for a golfing language. If you want a vectorized version of integer partitions, then this element only does that if there's another list at the same level as the integers of whom you want partitions, which seems unlikely.

With #1870, the integer partitions overload may be moved to another element entirely, which would help with resolving this issue.