SystemUI: Add support for timeout-reboot

By exploiting the already existing implementation used in Keyguard
to "lock" the device after a specific timeout has been reached
we add our own custom action that starts right when the display
is in the "locked" state and stops when we enter the "exit"
phase of keyguard ( aka unlocked )

Also cancel reboot timeout when unlocking without a secure lock screen.
Add a debugging statement to make this easier to troubleshoot (needs
`adb shell setprop persist.log.tag.Keyguard DEBUG`).

Issue: calyxos#1683
Co-authored-by: Tommy Webb <tommy@calyxinstitute.org>
Change-Id: I23170e5ec3ae296a4aa1d9c1793d61c8399c4d54