Add ability to make text join an existing bullet list

Intended behaviour specification

If you have:

Pressing the numbered bullet list toolbar button or the Ctrl + Shift + B keyboard shortcut at "third" should produce:

Similarly if the text is between two numbered lists:

We should get:

If there is a nested ordered list preceding the text:

Then:

This behaviour should activate if the cursor is:

• anywhere among the word "third"
• if the word "third" is wholly selected