Map META+L to lock the device

Cherry picked Ia928468318ba26ec19e4bb7aaf19c0f5a095d616 to master due to b/286408867.

Code was merged via `-s ours` and is missing even though the sha exists on the target branch. Cherry pick is required to bring in the code.

Manually remove the "Merged in" directive to allow for downstream propagation.

Fixes: 246657706
Test: META+L -> lock and go to the lockscreen
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:19fa8890c7f0c926ea70116b825ba0bf8047c744)
Change-Id: I0c4cd811ed6b1bab5dba18156727ce3702058552