This patch adds more fine grained information in ObjFile about PDB type server dependencies and precomp OBJ dependencies.
Dependencies are required to be loaded & merged first, before any dependent OBJ that relies on it.
Before, dependencies were discovered and loaded along the way, when the type stream for a given OBJ was being merged (in PDB.cpp).
This patch is part of ground work towards parallelizing the type merging. The objective is to split PDBLinker::addObjFile into several smaller parallelizable pieces. See D59226 for the overall intention.