deprecate concatenating `[...]`

```jlcon
julia> [1:2, 3]
WARNING: [a,b] concatenation is deprecated; use [a;b] instead
3-element Array{Int64,1}:
 1
 2
 3

julia> [1:2]
WARNING: [a] concatenation is deprecated; use [a;] instead
2-element Array{Int64,1}:
 1
 2
```

ref #2488, #3737, #7941