Revert "Drop width from sizing utils given .col- classes can do the same thing (follow up to #22376)"

This reverts commit 2f21403a93.

scss/_variables.scss

@@ -148,7 +148,7 @@ $spacers: (
   5: ($spacer * 3)
 ) !default;
 
-// This variable affects the `.h-*` classes.
+// This variable affects the `.h-*` and `.w-*` classes.
 $sizes: (
   25: 25%,
   50: 50%,

scss/utilities/_sizing.scss

@@ -1,6 +1,6 @@
 // Width and height
 
-@each $prop, $abbrev in (height: h) {
+@each $prop, $abbrev in (width: w, height: h) {
   @each $size, $length in $sizes {
     .#{$abbrev}-#{$size} { #{$prop}: $length !important; }
   }