[MLIR] Simplify semi-affine expressions using flattening

For the semi affine expressions, whenever rhs of a floordiv, ceildiv, mod
or product expression is a symbolic expression, we introduce a local variable
representing the result, and store the floordiv/ceildiv, mod or product
affine expression in LocalExprs. In this way the expression is flattened,
and trivial addition and subtraction related simplifications are performed.
Also rule based matching for detecting and transforming "expr - q * (expr floordiv q)"
to "expr mod q", where q is a symbolic exxpression, in simplifyAdd function.

Differential Revision: https://reviews.llvm.org/D112808