Update the BackgroundThread dependency

Need to use the BackgroundThread from modules-utils-backgroundthread
only after we move to the CrashRecovery module. But till the time we
ramp up the flag, we cannot use it directly.
Copying BackgroundThread to local utils for now.
Added a TODO to move it later.

Bug: b/289203818
Test: atest PackageWatchdogTest:com.android.server.PackageWatchdogTest
(cherry picked from https://android-review.googlesource.com/q/commit:160cb21a429400a0a3d3dff8f879e2fa8a608763)
Merged-In: I40b919bbe7a410eab48d099e30e5c54095731cac
Change-Id: I40b919bbe7a410eab48d099e30e5c54095731cac