fuzzer: modernize FuzzedDataProvider conversions (#177794) This change modernizes FuzzedDataProvider.h now that C++17+ is standard in LLVM. Replace the runtime if with if constexpr in ConvertUnsignedToSigned Make the unsigned/signed comparison explicit by casting TS::max() to TU GitOrigin-RevId: 1ce7a8159352e903f1dab50ff340fcd32a84cf63