LMS-2323 Prevent deletion of <num> element in a Step

Feature summary request

Re-insert the Step <num> if it is deleted, or prevent the deletion of <num> element in a Step - the <num> element of a Step should be mandatory.

Background

Currently, Lawmaker is not protecting the Step <num> as it happens with other elements such as subsections etc. This means that users can delete the <num> and add multiple sentences within a Step, ultimately producing bad XML.

When a user tries to delete a Step <num>, we should be forcing the Step <num> to be re-inserted.

Original Description

Whilst reviewing a UKSI that failed to transform in the bundle (https://tsoltd.atlassian.net/browse/LEGDEV-6106 ), Jim noticed the following:

I don’t think the Akoma Ntoso is right here. There are siblings between Steps that have no number:

<hcontainer name="step"><num>Step 4</num> <content /> </hcontainer> <hcontainer name="step"> <content /> </hcontainer> <hcontainer name="step"> <num>Step 5</num> <content/> </hcontainer>

The root of the issue was probably that the user wanted to put two sentences inside one Step. However, at the moment, the only way to insert another sentence inside a Step (or anywhere else) is by pressing Shift+Enter - there is no entry in the CCA to add another sentence (<p>). Therefore, we assume that the user did not know that an additional sentence could be inserted with Shift+Enter, and so decided to add a new step and deleted the step number in order to insert a new sentence within the Step.