Fix paragraph-in-table-cell spacing in rich-text editor

What does this MR do and why?

Fixes Paragraphs within tables show differently betwe... (#587871 - closed). We have some RTE-specific styles that try to remove padding from the bottom of only children inside table cells, list items, definition list items, etc. This doesn't work for paragraphs within table cells, because they're all considered only children given their structure in ProseMirror:

They're all only children of their NodeViewWrapper.

The CSS was last changed 7730ff65 to better support list items, so split the table cells styles away and target them correctly.

Screenshots or screen recordings

The paragraphs within the table cell now match the actual render when you save.

Before	After

How to set up and validate locally

1. Put the reproducer in a work item or MR description or note:

   Here's a table with cells containing multiple paragraphs:
   
   <table>
   <tr>
   <th>aw</th>
   <th>awa</th>
   </tr>
   <tr>
   <td>
   
   A single paragraph.
   
   A second paragraph!
   </td>
   <td>Nyonk.</td>
   </tr>
   </table>

2. Note it looks like "Before" in the rich-text editor.
3. Check this branch out. The CSS might live update if you're lucky, otherwise reload.
4. Note it now looks like "After".
5. Kui imeline!

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