Record in the newtab ping when the Customize panel opens, when one of
its subpanels opens and which one, and when "Explore more themes" is
clicked in the themes subpanel. The CustomizeMenu component records the
two open events at the point where the panel becomes visible, so every
way of opening it counts the same way, whether from the customize
button, a message, or the widgets context menu. The "Explore more
themes" button reports its click as a user event, the way the other
New Tab clicks reach the TelemetryFeed module.
The panel open reuses the `SHOW_PERSONALIZE` user event name, so the
seven entry points that already sent that event are changed to stop
sending it. Nothing was listening for the event before this patch, and
now that the TelemetryFeed module is aware of it, leaving those
dispatches in place would count every open twice.
Differential Revision: https://phabricator.services.mozilla.com/D324869
Nina Pypchenko
5bc47f3a9e