Implement the conversion between SDBMExpr and AffineExpr

    Since SDBM expressions are a subset of affine expressions, they can be
    converted to affine expressions in a straightforward way.  The inverse
    conversion may fail when the affine expression is not an SDBM.  Implement the
    inverse convresion assuming affine expressions are simplified and
    canonicalizied, detect subtractive and multiplicative forms of the stripe
    operation.

--

PiperOrigin-RevId: 245494735