support AVX instruction set at CPUMath native

[frank-dong-ms-zz]

In CPUMath native we only support SSE.
In dotnet framework and dotnet core 2.1 we are using CPUMath native directly which means we only have SSE.
In dotnet core 2.2 or later version, dotnet core supports hardware Intrinsics so have support for both AVX and SSE.

Support AVX in CPUMath native will have performance benefit as well as generates identical result from different dotnet framework version using.

[ericstj]

Supporting AVX in CPUMath native isn't interesting since we're using intrinsics with AVX on the latest frameworks.