AVX2 optimized code for AstroBWT

Added "astrobwt-avx2" parameter in config.json, it's turned off ("false") by default.

4-5% speedup on CPUs with proper AVX2 support (AMD Ryzen starting with Zen2, Intel Core starting with Haswell).

There will be no speedup on the following CPUs:

- Intel Pentium/Celeron don't support AVX2
- AMD Zen/Zen+ have only half-speed AVX

GCC compiled version is faster without AVX2, MSVC compiled version is faster with AVX2

src/backend/cpu/CpuLaunchData.cpp

@@ -39,6 +39,7 @@ xmrig::CpuLaunchData::CpuLaunchData(const Miner *miner, const Algorithm &algorit
     hwAES(config.isHwAES()),
     yield(config.isYield()),
     astrobwtMaxSize(config.astrobwtMaxSize()),
+    astrobwtAVX2(config.astrobwtAVX2()),
     priority(config.priority()),
     affinity(thread.affinity()),
     miner(miner),