[mlir][Interfaces][NFC] `ValueBoundsConstraintSet`: Add columns for constant values/dims

`ValueBoundsConstraintSet` maintains an internal constraint set (`IntegerRelation`), where every analyzed index-typed SSA value or dimension of a shaped type is represented with a dimension/symbol. Prior to this change, index-typed values with a statically known constant value and static shaped type dimensions were not added to the constraint set. Instead, `getExpr` directly returned an affine constrant expression.

With this commit, dynamic and static values/dimension sizes are treated in the same way: in either case, a dimension/symbol is added to the constraint set. This is needed for a subsequent commit that adds support for branches.