[mlir][SCF][NFC] `ValueBoundsConstraintSet`: Simplify `scf.for` implementation (#87862)

This commit simplifies the implementation of the
`ValueBoundsOpInterface` for `scf.for` based on the newly added
`ValueBoundsConstraintSet::compare` API and adds additional
documentation.

Previously, the interface implementation created a new constraint set
just to check if the yielded value and iter_arg are equal. This was
inefficient because constraints were added multiple times (to two
different constraint sets) for ops that are inside the loop.

Note: This is a re-upload of #86239.