R1:6a9dd61c427b

Make collapsed inlines more useful and anchor target highlights more accurate

Summary:
Ref T12616. Fixes T11648. Currently, we snug up replies with a negative margin (from T10563) but this throws off the anchor highlighting.

Instead:

- Remove padding from these dolumns.
- Use margins on the stuff inside them instead.
- Less margins for replies.
- Less margins for collapsed comments.
- Show some text for collapsed comments.

Test Plan:
{F4960890}

{F4960891}

Reviewers: chad

Reviewed By: chad…