[NFC][ScopBuilder] Move buildSchedule and its callees to ScopBuilder or ScopHelper

[NFC][ScopBuilder] Move buildSchedule and its callees to ScopBuilder or ScopHelper

Scope of changes:
1. Moved buildSchedule functions to ScopBuilder.
2. Moved combineInSequence function to ScopBuilder.
3. Moved mapToDimension function to ScopBuilder.
4. Moved LoopStackTy to ScopBuilder.
5. Moved getLoopSurroundingScop to ScopHelper.
6. Moved getNumBlocksInLoop to ScopHelper.
7. Moved getNumBlocksInRegionNode to ScopHelper.
8. Moved getRegionNodeLoop to ScopHelper.

Differential Revision: https://reviews.llvm.org/D64223

llvm-svn: 366377