Fix #3020: Add spacing helpers for all sides

sass/helpers/spacing.sass

@@ -12,6 +12,9 @@ $spacing-values: ("0": 0, "1": 0.25rem, "2": 0.5rem, "3": 0.75rem, "4": 1rem, "5
 
 @each $property, $shortcut in $spacing-shortcuts
   @each $name, $value in $spacing-values
+    // All directions
+    .#{$shortcut}-#{$name}
+      #{$property}: $value !important
     // Cardinal directions
     @each $direction, $suffix in $spacing-directions
       .#{$shortcut}#{$suffix}-#{$name}

sass/utilities/_all.sass

@@ -3,7 +3,7 @@
 
 @import "initial-variables.sass"
 @import "functions.sass"
-@import "derived-variables.scss"
+@import "derived-variables.sass"
 @import "animations.sass"
 @import "mixins.sass"
 @import "controls.sass"