This PR adds SMT-LIB operators to detect overflow
`BitVec.(umul_overflow, smul_overflow)`, according to the definitions
[here](https://github.com/SMT-LIB/SMT-LIB-2/blob/2.7/Theories/FixedSizeBitVectors.smt2),
and the theorems proving equivalence of such definitions with the
`BitVec` library functions (`umulOverflow_eq`, `smulOverflow_eq`).
Support theorems for these proofs are `BitVec.toInt_one_of_lt,
BitVec.toInt_mul_toInt_lt, BitVec.le_toInt_mul_toInt,
BitVec.toNat_mul_toNat_lt, BitVec.two_pow_le_toInt_mul_toInt_iff,
BitVec.toInt_mul_toInt_lt_neg_two_pow_iff` and `Int.neg_mul_le_mul,
Int.bmod_eq_self_of_le_mul_two, Int.mul_le_mul_of_natAbs_le,
Int.mul_le_mul_of_le_of_le_of_nonneg_of_nonpos, Int.pow_lt_pow`. The PR
also includes a set of tests.
Co-authored by @tobiasgrosser.
---------
Co-authored-by: Tobias Grosser <tobias@grosser.es>
Co-authored-by: Tobias Grosser <github@grosser.es>
Co-authored-by: Siddharth <siddu.druid@gmail.com>
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