[incfs] Make native library extraction async

IncrementalService can create the library files beforehand, but
delay filling in their data. As it takes quite a while in
general (over a second in cases when the phone is busy), it's
better to run the unzipping and filling in a separate thread
and only make sure it finishes before the whole installation
process is complete.
This speeds up the megacity.apk installation by ~250-300ms,
1000-1100ms -> 750-800ms

Bug: 153513507
Test: adb install megacity.apk

Change-Id: Ia44f7e45b9e0abaebdfb6fe5352f9dcf29ab4ece