Record when a user ungroups the tabs of a tab group.
We ungroup an entire group when the user selects the "Ungroup tabs" context menu item on the tab group, but we also do that if the user cancels out of tab group creation context menu. We are particularly interested in understanding when users cancel out of the creation process. This may give us a better indicator about accidental tab group creation, e.g. when the user intended to drag and drop to move a tab but ended up creating a tab group from two tabs.
Differential Revision: https://phabricator.services.mozilla.com/D247633
b7d69dd476