Selecting / deselecting large amount of items with MultiDrag plugin, extremely sluggish due to inefficient filtering process.

[twilson90]

I have a sortable list with hundreds of items. If I select 100 items with shift + click, there is very noticable delay... If I have 1000+ items (for testing purposes) and select all of them, it took 20-40 seconds.

The issue lies here: https://github.com/SortableJS/Sortable/blob/3696da44b57c81dbe441aa48af28b0c38f6b11e2/plugins/MultiDrag/MultiDrag.js#L347-L357

Here's a screenshot from the performance tab in developer tools:

With each iteration through the list it becomes slower. There are more efficient ways of doing this.