Bug
1878434 - Add the `awesomebar.{engagement, abandonment}` events.
This commit:
* Sends the new `awesomebar.{engagement, abandonment}` events when the
user finishes interacting with the awesomebar. These events match
iOS's events of the same name, and Desktop's
`urlbar.{engagement, abandonment}` events.
* Removes the `engagement_abandoned` extra key for the
`awesomebar.{sponsored, non_sponsored}_suggestion_impressed` events,
since they're specific to AMP and Wikipedia suggestions, and are
subsumed by the new events.
This is the first step toward unifying our awesomebar search telemetry
on all our platforms.