Writes region description to shmem file in the launcher.

The VSoCMemoryLayout needed to show accurate size values on all
host processes, which gets complicated because the launcher may resize
some regions. With this change VSoCMemoryLayout no longer holds the
size information, it is instead calculated on the launcher and
persisted to the shared memory file, where every host process can read
it from.

Bug: 110539298
Test: local and gce runs
Change-Id: Id7feda309ff4ee3c432523cc820f6d6c4c2dbb41