The improvements are:
* Add an aria-label to the like/read count buttons below posts to
indicate what they mean and do.
* Add aria-pressed to the like/read count buttons to make it clear to screen
readers that these buttons are toggleable.
* Add an aria-label to the list of avatars that's shown when post likes
or readers are expanded so that screen reader users can understand what
the list of avatars means.
fd26facdf3