Synchronize native ApkAssets data

If an ApkAssets is created and destroyed before being put into an
AssetManager, the native layer may not have been synchronized in the
thread that does Java object finalization. So when the Java object gets
deleted on the finalization thread, it may see old/unallocated native
data and not delete the native object correctly.

Similar to how we already lock on the native AssetManager whenever
entering the JNI layer, we should also do the same for ApkAssets.

Bug: 186528775
Test: boot and no crashes
Change-Id: I5fcb9e788a9e3cb8baeb92fa6efc882d5bbbf0b0