Updated asmjit & adapted to its latest changes

[kobalicek]

• Updated asmjit, which uses a different coding style
• Modified code that used SSE versions of some vector instructions instead of AVX versions (conversion, moves, scalar operations)
• Modified code that relied on Xmm/Ymm/Zmm to simply use Asmjit's x86::Vec operand in places where possible (requires more future work to remove the FBGEMMs Xmm/Ymm/Zmm substitutes)
• Simplified code paths that were using avx2 and avx512
• Simplified the use of a JitRuntime - ideally there should be only one around to reduce the number of memory mappings, so now there is only one shared JitRuntime - it doesn't need a lock as it's thread-safe

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[kobalicek]

Take it or dump it - it was just a little exercise for me to understand how much time is required per project to adapt to the new version of AsmJit. The rest of the changes are related to a correct use of AsmJit and a correct use of instructions in AVX/AVX-512 mode.