Enhancement: Stats modal in admin bar for individual posts and pages

### Impacted plugin

Jetpack

### What

The current stats icon in the admin bar only shows total site stats and links to the general stats page. It would be a more useful and intuitive experience for users if there was a modal displayed on hover that showed a highlight of stats for the individual post or page you are viewing. Clicking the icon would take you to the complete stats for the specific post or page.

### How

Here is a quick concept using a screenshot of the Email Stats for a post. Including Views, Likes, Comments in addition to the email stats would be ideal.

Start at the Jetpack admin bar stats icon and compare its current general-stats link with the individual post or page being viewed. Done means hovering shows a modal with post- or page-specific Views, Likes, Comments, and email highlights, while clicking opens complete stats for that specific post or page.

Written by the indexing model from the issue text.