Another small step forward to move VPlan stuff outside of LoopVectorize.cpp.
- VPlanBuilder.h is renamed to LoopVectorizationPlanner.h
- LoopVectorizationPlanner class is moved from LoopVectorize.cpp to LoopVectorizationPlanner.h
- LoopVectorizationCostModel::VectorizationFactor class is moved to LoopVectorizationPlanner.h (used by the planner class) --- this needs further streamlining work in later patches and thus all I did was take it out of the CostModel class and moved to the header file.
- The callback function had to stay inside LoopVectorize.cpp since it calls an InnerLoopVectorizer member function declared in it.
Next Steps: Make InnerLoopVectorizer, LoopVectorizationCostModel, and other classes more modular and more aligned with VPlan direction, in small increments.
Previous Step was: https://reviews.llvm.org/D41045.