[Profile Showcase] Custom positioning when reordering a filtered In showcase list

[alexjba]

Description

Design

The user is free to drag items into the showcase and re-order whilst in the search filtered state. 

We should follow Sheets / Excel logic for defining the relative position of moved items once the search filter is removed. 

In essence this logic is as follows:

Moving an item down the list while filter applied
When the filter is removed the item is left directly under under the item it was moved below while in the filtered state (we can only infer which of the visible list items they wish to move the list item below).

Moving an item up the list while filter applied
When the filter is removed the item is left directly above the item it is moved above while in the filtered state (we can only infer which of the visible list items they wish to move the list item above).

Note for development: Re-enable the DND

[alexjba]

Depends on #13508