fix bullet list render compatibility with latest ms word version

[jgiacomello]

Description

I noticed that creating a file from html unordered lists rendered symbols differently than the MS Word default.

Example code:

<ul>
    <li>lista 1</li>
    <li>lista 1<ul>
            <li>lista 2</li>
            <li>lista 2<ul>
                    <li>lista 3</li>
                </ul>
            </li>
            <li>lista 2</li>
        </ul>
    </li>
    <li>lista 1</li>
    <li>lista 1</li>
</ul>

result with current library version:

result with fixes:

I'm using this MS Word version: Microsoft® Word for Microsoft 365 MSO (Version 2502)

Checklist:

• My CI is 🟢
• I have covered by unit tests my new code (check build/coverage for coverage report)
• I have updated the documentation to describe the changes
• I have updated the changelog

[coveralls]

coverage: 96.767%. remained the same
when pulling 7faa833 on jgiacomello:bullet_list_render
into 6ca8c9f on PHPOffice:master.