[NFC][ScopBuilder] Move RecordedAssumptions vector to ScopBuilder

Scope of changes:

1) Moved RecordedAssumptions vector to ScopBuilder. RecordedAssumptions are used only for Scop constructions.
2) Moved definition of RecordedAssumptionsTy to ScopHelper. It is required both by ScopBuilder and SCEVAffinator.
3) Add new function recordAssumption to ScopHelper. One of its argument is a reference to RecordedAssumption vector. This function is used by ScopBuilder and SCEVAffinator.
4) All RecordedAssumptions are created by ScopBuilder. isl::pw_aff
objects for corresponding SCEVs are created inside ScopBuilder. Scop
functions do not record any assumptions. Scop can use isl::pw_aff
objects which were created by ScopBuilder.
5) Removed functions for handling RecordedAssumptions from Scop class.
6) Removed constness from getScopArrayInfo functions.
7) Replaced SCEVVisitor struct from SCEVAffinator with taylored version, which allow to pass pointer to RecordedAssumptions as function argument.

Differential Revision: https://reviews.llvm.org/D68056