Add make-col-auto mixin (#29367)

scss/mixins/_grid-framework.scss

@@ -41,9 +41,7 @@
       }
 
       .col#{$infix}-auto {
-        flex: 0 0 auto;
-        width: auto;
-        max-width: 100%; // Reset earlier grid tiers
+        @include make-col-auto();
       }
 
       @for $i from 1 through $columns {

scss/mixins/_grid.scss

@@ -45,6 +45,12 @@
   max-width: percentage($size / $columns);
 }
 
+@mixin make-col-auto() {
+  flex: 0 0 auto;
+  width: auto;
+  max-width: 100%; // Reset earlier grid tiers
+}
+
 @mixin make-col-offset($size, $columns: $grid-columns) {
   $num: $size / $columns;
   margin-left: if($num == 0, 0, percentage($num));