Combine all the highpoly pixel arrays into a single array with a lookup
object_id for each of the highpoly objects.
Note: This changes the Bake API, external engines should refer to the
bake_api.c for the latest API.
Many thanks for Sergey Sharybin for the complete review, changes
suggestion and feedback. (you rock!)
Reviewers: sergey
Subscribers: pildanovak, marcclintdion, monio, metalliandy, brecht
Maniphest Tasks: T41092
Differential Revision: https://developer.blender.org/D772