Refactor AffineExprFlattener and move FlatAffineConstraints out of IR into

Analysis - NFC

- refactor AffineExprFlattener (-> SimpleAffineExprFlattener) so that it
  doesn't depend on FlatAffineConstraints, and so that FlatAffineConstraints
  could be moved out of IR/; the simplification that the IR needs for
  AffineExpr's doesn't depend on FlatAffineConstraints
- have AffineExprFlattener derive from SimpleAffineExprFlattener to use for
  all Analysis/Transforms purposes; override addLocalFloorDivId in the derived
  class

- turn addAffineForOpDomain into a method on FlatAffineConstraints
- turn AffineForOp::getAsValueMap into an AffineValueMap ctor

PiperOrigin-RevId: 235283610