Start a new keyguard session on device sleep

One nuance of this is that a new keyguard session
will start if the user is on the lock screen and then
double presses the power button to launch camera due to the
following sequence of events:

[0ms] user is on the lock screen in KG session #1
[1ms] first power button press => device starts to
go to sleep, so new keyguard session begins KG session #2
[2ms] second power button press => camera is launched,
screen stays on instead of finishing going to sleep

Test: enable SessionTracker logs, see start and end
boundaries of Keyguard is update to include a new session
when the device goes to sleep
Test: atest SessionTrackerTest
Bug: 242628816

Change-Id: I40bdf7f746b7086bc9683f816e00913cd0fd49bf