RTF Writer: Create ListItemRun

[rasamassen]

Description

ListItemRun now works!

Depends on #2821

Limitations

• In the Library, there's currently no way to pass a fontStyle for the whole ListItemRun, nor for TextRun. Without being able to pass a fontStyle to the whole Run and then specify specific changes within the run, it makes it much harder to make small changes. Let's say I want a list that's all size => 22, color => purple, bold => true, but there's one little item I want to underline. I'd have to either pass all the variables on every line of the run or I'd have to setup two different fontStyles. It would be simpler to setup one fontStyle and then pass the small change as a custom fontStyle where DIFF would override the default for the run (but if no change, default still applies).

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: 96.765% (+0.008%) from 96.757%
when pulling eebb61a on rasamassen:ListItemRun
into 0ab0b49 on PHPOffice:master.