Integrate libsnapshot with the boot control HAL.

This patch translates UpdateState states into a MergeStatus from
IBootControl 1.1, and asks the HAL to store it. Unfortunately this patch
has to work around a few issues.

The first issue is that Soong doesn't allow including only the headers
from a HAL. The second issue is that entraining the headers requires
linking to libraries that would otherwise not be needed in init.

To address this, we now have three ways of linking to libsnapshot:
  1. libsnapshot - Has access to gsid and HALs.
  2. libsnapshot_nobinder - Has access to HALs, but not binder (for
                            recovery).
  3. libsnapshot_init - Does not use binder or HALs.

The HAL code is #ifdef'd behind LIBSNAPSHOT_USE_HAL and we make use of
forward declarations and dependency injection to minimize its spread.

Bug: 139154945
Test: libsnapshot_test gtest
Change-Id: I21ffd8a79a43d0589f2f71f346ac1b019584a183