Adjust button mixin to assure all buttons have consistent base layout

Make sure all buttons—including icon-only buttons—get a flex layout. For
icon-only buttons, this ensures that the icon is centered on the button,
which is relevant especially when a `min-width` or `min-height` is
applied.

src/styles/shared/components/buttons/mixins.scss

@@ -83,11 +83,11 @@
   font-weight: 700;
   white-space: nowrap; // Keep multi-word button labels from wrapping
 
-  @if map.get($options, 'withLayout') {
   display: flex;
   justify-content: center;
   align-items: center;
 
+  @if map.get($options, 'withLayout') {
     &--icon-left svg {
       margin-right: map.get($options, 'margin');
     }