Detect dismissals on the lockscreen surface

When users dismiss notifications from the lockscreen, they're currently getting attributed to being dismissed from the shade. This change distinguishes lockscreen dismissals from shade dismissals for more specific and accurate metrics.

(These dismissal surfaces are already translated to cancellation reasons in NotificationRecordLogger.)

Bug: 234507856
Test: statsd_testdrive
Change-Id: I80539025e2d4d7bacbcda59133a85d06d4690a35