Adwaita: row transitions and spacing

- no fading out of row hovers. Many feel like it's a slow
  refresh rather than intentional effect.
- give some margin to navigation lists

Fixes https://gitlab.gnome.org/GNOME/gtk/-/issues/3434

gtk/theme/Adwaita/_common.scss

@@ -3249,12 +3249,8 @@ list {
 }
 
 row {
-  transition: all 150ms $ease-out-quad;
-
   @include focus-ring();
 
-  &:hover { transition: none; }
-
   &.activatable {
     &.has-open-popup, // this is for indicathing which row generated a popover see https://bugzilla.gnome.org/show_bug.cgi?id=754411
 
@@ -3614,7 +3610,7 @@ separator.sidebar {
     min-height: 36px;
     padding: 0 8px;
     border-radius: $menu-margin;
-    margin: 0 $menu-margin;
+    margin: 0 $menu-margin 2px;
 
     &:hover,
     &:focus-visible:focus-within {