Format parameter lists with trailing commas like argument lists.

test/comments/functions.unit

Index: test/comments/functions.unit
diff --git a/test/comments/functions.unit b/test/comments/functions.unit
index b2d0bc91d33ee26ebc20df1376dd48cca204440e..00c235b2dc6e827003e32724a1291b4dc207bebe 100644
--- a/test/comments/functions.unit
+++ b/test/comments/functions.unit
@@ -126,4 +126,21 @@ main() {
 <<<
 main() {
   // comment
+}
+>>> comment before "]" with trailing comma
+function([parameter,/* c */]) {;}
+<<<
+function([
+  parameter,
+  /* c */
+]) {
+  ;
+}
+>>> comment before ")" with trailing comma
+function([parameter,]/* c */) {;}
+<<<
+function([
+  parameter,
+] /* c */) {
+  ;
 }