Changing the handled operators in bv2int preprocessing pass (#4970)

Changing the handled operators in bv2int preprocessing pass (#4970)

Some of the bit-vector operators are directly translated to integers, while others are eliminated before the translation.
This PR changes the set of operators that we eliminate (and as a consequence, also the set of operators that we handle directly):

The only bit-wise operator that is translated is bvand. The rest are now eliminated.
bvneg is now eliminated.
The various division operators are still eliminated, but using different rewrite rules.
zero-extend and sign-extend are now handled directly.
shifting is changed to favor ITEs over non-linear multiplication.