R1:e8126fa95858

Don't mangle inline comments with tables in them in Differential

Summary:
Fixes T3814. Broadly, remarkup tables in inline comments did not work properly. I ran into several messes here and cleaned up some of them:

- Some of this code is doing `JX.$N('div', {}, JX.$H(response.markup))`, to turn an HTML response into a node, passing that around, and then doing junk with it. This is super old and gross.
- The slightly more modern pattern is `JX.$H(response.markup).getFragment().firstChild`, but this…