Make loadDocumentFromInput in AbstractRuleBasedDocxWriter overridable

[ingomohr]

loadDocumentFromInput in AbstractRuleBasedDocxWriter is protectected and can be overridden.

However, the method it uses in its default impl is private - so, if subclasser would want to use that method too, they'd have to copy it.

And there's no reason to have that method private.

Task

Make the private method protected.

[ingomohr]

Done

• CI ✔️
• Changed only that methods access modifier (directly on master)