Reland: Rework platform version to hide codenames.

The public platform version no longer can be a codename, it is
always the most recently released platform.  A new build property
and API provides either the offical version or the current codename
as appropriate.  This will avoid breaking apps that look at the
platform version while development is under a codename.

Changes from the original version:
- Logic for emitting system properties has also been added to
  buildinfo_common.sh to make sure that ro.${partition}.build.*
  are consistent with ro.build.*.
- We also use PLATFORM_VERSION_LAST_STABLE as the value set in the
  boot image os_version header / hash tree additional headers to
  ensure they match with the ro.build.version.release system property.
  This is hopefully a temporary workaround while we stop using the
  system property for this purpose.

Bug:  143175463
Test: manual
Change-Id: Iaeefb35137de01c6ea57115d8830dd9bc30eccba