See comments on https://gerrit.wikimedia.org/r/195902
`<td><p>foo<p></td>` serializes to `|foo`, which means it doesn't roundtrip html -> wt -> html because the `<p>`-wrapping disappears:
```
$ echo '<table><tr><td><p>foo</p></td></tr></table>' | tests/parse.js --html2html --normalize
<table>
<tbody>
<tr>
<td>foo</td>
</tr>
</tbody>
</table>
```
But in fact we can recover the `<p>`-wrapping by adding a newline after the `|`:
```
$ ( echo '{|' ; echo '|' ; echo 'foo' ; echo '|}' ) | tests/parse.js --normalize
<table>
<tbody>
<tr>
<td>
<p>foo</p>
</td>
</tr>
</tbody>
</table>
```
So there is a way to say whether `<p>`-wrapping should happen in wikitext or not -- we need to emit a leading `\n` if we want `<p>`-wrapping. This is a WTS bug. The fix for T88318 fixed a different bug ( `<td><meta/>-</td>` for instance ), but we should fix `<p>`-wrapping inside `<td>` properly by re-adding the missing newline after the `|`.