Sort the children of a parent node after either deleting or moving a child node

[manutdkid77]

Prerequisites

• [x] I have added steps to test this contribution in the description below

This fixes #17273

Description

• When a new document node A is created under a parent node, it is assigned a SortOrder value of 0.
• Now if you created another document node B under the parenr node, it is assigned a SortOrder value of 1.
• Now delete node A
• Create a new node C, here the SortOrderExists looks to find any item with sortOrder as 0.
• But the SortOrderExists can't find such an item with SortOrder as 0, so it returns false, and this results in setting the SortOrder as 0
• My solution is to recalculate the Sort after deletion or move operation of a document node.