Integer set + operands / affine if op canonicalization

- turn canonicalizeMapAndOperands into a template that works on both
  sets and maps, and use it to introduce a utility to canonicalize an
  affine integer set and its operands
- add pattern to canonicalize affine if op's.
- rename IntegerSet::getNumOperands -> IntegerSet::getNumInputs to be
  consistent with AffineMap
- add missing accessors for IntegerSet

Doesn't need extensive testing since canonicalizeSetAndOperands just
reuses canonicalizeMapAndOperands' logic, and the latter is tested on
affine.apply map + operands; the new method works the same way on an
integer set + operands of an affine if op for example.

Signed-off-by: Uday Bondhugula <uday@polymagelabs.com>

Closes tensorflow/mlir#112

COPYBARA_INTEGRATE_REVIEW=https://github.com/tensorflow/mlir/pull/112 from bondhugula:set-canonicalize eff72f23250b96fa7d9f5caff3877440f5de2cec
PiperOrigin-RevId: 267532876