Introduce Deaffinator pass.

This function pass replaces affine_apply operations in CFG functions with
sequences of primitive arithmetic instructions that form the affine map.

The actual replacement functionality is located in LoweringUtils as a
standalone function operating on an individual affine_apply operation and
inserting the result at the location of the original operation.  It is expected
to be useful for other, target-specific lowering passes that may start at
MLFunction level that Deaffinator does not support.

PiperOrigin-RevId: 222406692