[mlir][Interfaces] `LoopLikeOpInterface`: Expose tied loop results (#70535)

Expose loop results, which correspond to the region iter_arg values that
are returned from the loop when there are no more iterations. Exposing
loop results is optional because some loops (e.g., `scf.while`) do not
have a 1-to-1 mapping between region iter_args and op results.

Also add additional helper functions to query tied
results/iter_args/inits.