Add a privileged API for capturing and consuming bugreports

The API is mostly implemented; except for hooking up the listener
and handling an already running bugreport.

BugreportManager is the handle to the new API exposed to apps.

Generating bugreports requires root privileges. To limit the footprint
of the root access, the actual bugreport generation in Dumpstate binary,
is accessed as a oneshot service and dies after it finishes
running.

System server accesses Dumpstate via a binder interface since it does
not have root privileges.

Starting a oneshot service is done via setting a system property, which
needs to be done from system server. BugreportManagerService is the
new system server service that does this. BugreportManager calls into
BugreportManagerService via a binder interface, since the former is in
the app's process.

Both app to system server as well as system server to native service
calls are via implementations of IDumpstate binder interface.

Bug: 111441001
Test: builds. Flashed & verified it boots.
Test: wrote a test client (not included) and verified invoking
startBugreport works.

Change-Id: I4abeb753388c055c36ae0dd916af1ec8d40b7bf0