chore(mixins): enable passing extra transitionable props to some mixins

src/style/mixins.scss

@@ -68,7 +68,14 @@ $clickable-normal-state-transitions: (
     background-color var(--limel-clickable-transition-speed, 0.4s) ease,
     box-shadow var(--limel-clickable-transform-speed, 0.4s) ease,
     transform var(--limel-clickable-transform-speed, 0.4s)
-        var(--limel-clickable-transform-timing-function, ease)
+        var(--limel-clickable-transform-timing-function, ease),
+    // the property below can be used by consumer to pass
+    // one or more extra transition properties to the mixin,
+    // instead of overriding (or repeating) the whole transition rule
+    // which is applied by the mixin
+    // an example could be:
+    // `--limel-additional-clickable-transition-properties: opacity 0.2s ease, width 0.3s ease-out;`
+    var(--limel-additional-clickable-transition-properties)
 );
 
 @mixin is-elevated-clickable(