OMS: introduce the OverlayManagerService

Add a new system service to manage Runtime Resource Overlays. This will
offload the PackageManagerService and allow administration of overlay
packages while affected packages continue to execute.

Overlays can be enabled or disabled during runtime. Running applications
will re-create their ResourcesImpl objects and restart their activities
via the usual activity life cycle.

The order in which a set of overlays is loaded may also be changed
during runtime. The underlying mechanics are the same as for when an
overlay is enabled or disabled.

When an overlay changes state, e.g. becomes enabled, the
OverlayManagerService will broadcast one of the new intents
android.intent.action.OVERLAY_ADDED, *_CHANGED, *_REMOVED or
*.OVERLAYS_REORDERED.

Clients that wish to read information about overlays for users other
than themselves are required to hold the
android.permission.INTERACT_ACROSS_USERS_FULL permission. This mirrors
the protection level of PackageManager.getPackageInfo.

Clients that wish to change the information are required to
hold the permission android.permission.CHANGE_OVERLAY_PACKAGES.

Each pair of overlay package and corresponding target package is
respresented by a new OverlayInfo class. This class mirrors the
existing PackageInfo class.

Overlay packages are handled per Android user. The data is persisted in
/data/system/overlays.xml.

Co-authored-by: Martin Wallgren <martin.wallgren@sonymobile.com>
Signed-off-by: Zoran Jovanovic <zoran.jovanovic@sonymobile.com>
Bug: 31052947
Test: run tests from 'OMS: tests for OverlayManagerService'
Change-Id: I15325e173193df3240b8dc0a58c852fd7a3d5916