Fix Nested Content "second time dragging" issue

[kjac]

Prerequisites

• I have created an issue for the proposed changes in this PR, the link is: Dragging Nested Content items throws them out of place #3079
• I have added steps to test this contribution in the description below

Description

This PR ensures that the items in the Nested Content item list aren't thrown out of place when dragging them around.

To test it:

1. Drag an item twice in a Nested Content item list without reloading the page in between
2. Verify that the dragged item stays within the list while dragging - both times.

[emmaburstow]

Hi again @kjac ;-)

We'll have a good look at this work and let you know if we need anything. Thanks for the handy gif!

Emma, Community Pull Request team

[nul800sebastiaan]

Hey @kjac - while this may have fixed the second time dragging, I now seem to have a problem on the FIRST time dragging. This only happens after the page loads and you start dragging for the first time, everything seems fine after the first time. Once I click the icon to sort, the item I'm dragging just disappears. Is this something you can reproduce too? Maybe it's just me.

[kjac]

@nul800sebastiaan that's a scrolling issue. If you've scrolled your page down a bit, the initial offset of the dragged item is wrong. It fixes itself though as soon as you move the dragged item around in the list.

The issue is already present in the current version and isn't fixed by this PR 😄

[nul800sebastiaan]

@kjac Wonderful, I look forward to seeing another PR for that then! ;-)

Cool, I'll merge this because (indeed) it fixes what it is supposed to! 👍

[kjac]

Nice!