Support .grid + small in forms

scss/content/_form.scss

@@ -328,7 +328,13 @@ select {
 }
 
 // Helper
-:where(input, select, textarea) {
+$inputs: "input, select, textarea";
+
+@if ($enable-classes and $enable-grid) {
+  $inputs: $inputs + ", .grid";
+}
+
+:where(#{$inputs}) {
   + small {
     display: block;
     width: 100%;