* Renamed FileManifest to BuildManifest and FileManifestItems to BuildProducts, to more accurately reflect what they are.
* Removed ref qualifier when passing BuildManifest around; it's already a reference type, and not meant to be assigned to.
* Removed UAT's redundant copy of BuildManifest, since it already references the UBT assembly.
[CL 2406323 by Ben Marsh in Main branch]