Named parameters used as positional for builtins

This works:
```
std.makeArray(func=function(i) i, sz=5)
```
But this does not work:
```
std.makeArray(sz=5, func=function(i) i)
```
Error:
```
RUNTIME ERROR: Builtin function makeArray expected (number, function) but got (function, number)
        testdata/std.makeArrayNamed2.jsonnet:1:1-39
```

The names are checked, but then arguments are treated as positional anyway.