Improve deteriminism of simulateDrag

What does this MR do and why?

This MR addresses an issue identified in this comment where tests using the simulateDrag helper were very flaky.

• Instead of using setTimeout let's use requestAnimationFrame.
• Let's also wait a frame between moving and finishing.

Screenshots or screen recordings

Screencast_2021-11-24_20_19_42

How to set up and validate locally

1. Either on .com or locally, go to an issues board page which has 3 or more issues in the first list.

2. Remove the export function part of the simulate_drag.js. Copy and paste the simulate_drag.js contents into a browser console (see demo)

3. Run the following in the browser console:

   simulateDrag({
     scrollable: document.querySelector('body'),
     duration: 1000,
     performDrop: true,
     extraHeight: 0,
     from: {
       el: document.querySelectorAll('.board-list')[0],
       index: 0,
     },
     to: {
       el: document.querySelectorAll('.board-list')[0],
       index: 2
     }
   });

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.