Add a shell command to force the background dexopt job

Add 'bg-dexopt-job' command to 'adb shell cmd package' which will force
the background  dexopt job to run the optimizations immediately.

Note that the command only runs the background optimizer logic. It may
overlap with the actual job but the job scheduler will not be able to
cancel it. It will also run even if the device is not in the idle
maintenance mode.

Test: adb shell cmd package bg-dexopt-job
Bug: 32871170

(cherry picked from commit cb5f41ea)

Change-Id: I82c781d46fe16e7b7566a5b5ee91be723a2125cb

Merged-In: I8b0112074220b2e09baf13d842401ee1cf306a89