Create separate variables for each design system spacing scale value

In variables.scss the current representation of the spacing scale is the following:

$gl-spacing-scale: (
  0: 0,
  1: #{0.25 * $grid-size},
  2: #{0.5 * $grid-size},
  3: $grid-size,
  4: #{1.5 * $grid-size},
  5: #{2 * $grid-size},
  6: #{3 * $grid-size},
  7: #{4 * $grid-size},
  8: #{5 * $grid-size}
);

This representation was conceived with the purpose of automating the creation of utility classes. Since we are declaring such utilities manually, using this data structure is cumbersome. Let’s change it to separate variables:

$gl-spacing-scale-0: 0;
$gl-spacing-scale-1: 0.25 * $grid-size;
// etc