Harden named arguments if a hard split occurs in the positional ones.

test/splitting/function_arguments.stmt

 40 columns                              |
 >>> args before and after function forces nesting
 method(first,() {fn;},third);
 <<<
 method(
     first,
     () {
       fn;
     },
     third);
@@ skipping 149 matching lines @@
 obj.outer(obj.inner(() {
   body;
 }));
 >>> do nest because of nested many-arg method call
 obj.outer(argument, obj.inner(() {body;}));
 <<<
 obj.outer(
     argument,
     obj.inner(() {
       body;
-    }));
+    }));
+>>> force named args to split on positional function
+function(argument, () {;},
+    named: argument, another: argument);
+<<<
+function(
+    argument,
+    () {
+      ;
+    },
+    named: argument,
+    another: argument);