FlatAffineConstraints - complete TODOs: add method to remove duplicate /

trivially redundant constraints. Update projectOut to eliminate identifiers in
a more efficient order. Fix b/120801118.

- add method to remove duplicate / trivially redundant constraints from
  FlatAffineConstraints (use a hashing-based approach with DenseSet)
- update projectOut to eliminate identifiers in a more efficient order

(A sequence of affine_apply's like this (from a real use case) finally exposed
the lack of the above trivial/low hanging simplifications).

  for %ii = 0 to 64 {
    for %jj = 0 to 9 {
      %a0 = affine_apply (d0, d1) -> (d0 * (9 * 1024) + d1 * 128) (%ii, %jj)
      %a1 = affine_apply (d0) ->
        (d0 floordiv (2 * 3 * 3 * 128 * 128),
        (d0 mod 294912) floordiv (3 * 3 * 128 * 128),
        (((d0 mod 294912) mod 147456) floordiv 1152) floordiv 8,
        (((d0 mod 294912) mod 147456) mod 1152) floordiv 384,
        ((((d0 mod 294912) mod 147456) mod 1152) mod 384) floordiv 128,
        (((((d0 mod 294912) mod 147456) mod 1152) mod 384) mod 128)
          floordiv 128) (%a0)
      %v0 = load %in[%a1tensorflow/mlir#0, %a1tensorflow/mlir#1, %a1tensorflow/mlir#3, %a1tensorflow/mlir#4, %a1tensorflow/mlir#2, %a1tensorflow/mlir#5]
        : memref<2x2x3x3x16x1xi32>
    }
  }

- update FlatAffineConstraints::print to print number of constraints.

PiperOrigin-RevId: 225397480