[NFC][ScopBuilder] Move addRecordedAssumption to ScopBuilder
Scope of changes:
- Moved addRecordedAssumptions to ScopBuilder.
- Moved Assumption struct outside Scop class.
- Refactored addRecordedAssumptions function. Replaced while loop by
for range loop.
- Added function to clear processed Assumptions.
Differential Revision: https://reviews.llvm.org/D63572