Feature: Wrap nested lists in previous listitem instead of in a new listitem

[Placeprom]

Lexical version: 0.3.11

Current solution

Currently nested lists are added wrapped inside a new listitem:

<ol>
   <li>one</li>
   <li>
      <ol>
         <li>one.one</li>
         <li>one.two</li>
      </ol>
   </li>
   <li>two</li>
</ol>

This makes things like prefixes for nested list (1.1, 1.2 [...]) way harder to achieve. We can´t easily make use of incrementing css counters and autoincrements won´t work correctly since there is another list item in the first level list. Actually we need to set list-style-type:"none"; on nested lists to get rid of multiple (and incorrect) counters.

Alternative solution

An alternative solution would be to wrap the nested list inside the previous listitem.

<ol>
   <li>one
      <ol>
         <li>one.one</li>
         <li>one.two</li>
      </ol>
   </li>
   <li>two</li>
</ol>

This would allow us to achieve things like prefixes way easier since we can just use css counters which won´t get mixed up by a wrong number of listitems. We can also make use of the autoincrement since there is no wrong number of listitems in the previous list level.