Publicize: update checkboxes to show when a post was successfully posted on a Social Network

Right now you don't have a way to know whether Publicize was triggered for one of your published posts; the checkboxes are either available when the post hasn't been published yet, or all greyed out when the post is published. It'd be nice to display whether a post was published on each social network, and maybe add a link to said post.

Suggested here:
https://wordpress.org/support/topic/logging-what-publishing-was-successful/

Start by reading the linked WordPress support discussion and tracing the Publicize publishing flow; the issue does not identify files, tests, or entry points. Define the post-status data available for each social network before deciding how the checkbox state and optional link should be represented. Done means the published post clearly shows success per network and links to the remote post where available.

Written by the indexing model from the issue text.