x64Emitter: refactor, add some new AVX instructions
JitAsmCommon: remove a few redundant moves
JIT: load registers if they're going to be used later in the block
JIT: add more AVX support, reduce redundant XMM moves

10-20% reduction in typical compiled block size for float-heavy JIT blocks.
Merge pull request #1216 from FioraAeterna/movoptimizations

Add more AVX support, refactor emitter, reduce redundant XMM moves