Add will-change to improve scrolling perf (#5001)

app/javascript/styles/components.scss

@@ -1587,6 +1587,7 @@
   overflow-x: hidden;
   flex: 1 1 auto;
   -webkit-overflow-scrolling: touch;
+  will-change: transform; // improves perf in mobile Chrome
 
   &.optionally-scrollable {
     overflow-y: auto;