Fix misc bugs / TODOs / other improvements to analysis utils

- fix for getConstantBoundOnDimSize: floordiv -> ceildiv for extent
- make getConstantBoundOnDimSize also return the identifier upper bound
- fix unionBoundingBox to correctly use the divisor and upper bound identified by
  getConstantBoundOnDimSize
- deal with loop step correctly in addAffineForOpDomain (covers most cases now)
- fully compose bound map / operands and simplify/canonicalize before adding
  dim/symbol to FlatAffineConstraints; fixes false positives in -memref-bound-check; add
  test case there
- expose mlir::isTopLevelSymbol from AffineOps

PiperOrigin-RevId: 238050395