all: switch to the new fn arg syntax everywhere; add lots of vfmt -verify tests

vlib/strconv/format.v

@@ -846,7 +846,7 @@ pub fn v_sprintf(str string, pt ... voidptr) string{
 }
 
 [inline]
-fn v_sprintf_panic( idx, len int) {
+fn v_sprintf_panic(idx int, len int) {
 	if idx >= len {
 		panic('${idx+1} % conversion specifiers, but given only ${len} args')
 	}