For `Vector4.Transform(Vector4, Matrix4x4)` we had `5.22ns` to `2.46ns` (~53% faster)

For `Matrix4x4.Multiply(Matrix4x4, Matrix4x4)` its a bit less at `10.04ns` to `8.38ns` (~17% faster)

The main improvements tracked by: * https://github.com/dotnet/perf-autofiling-issues/issues/1144... * https://github.com/dotnet/perf-autofiling-issues/issues/1148... * https://github.com/dotnet/perf-autofiling-issues/issues/1146...

There are some more cases to be improved. `Matrix4x4.Multiply` in particular I need to update to use a proper SIMD implementation rather than its current scalar implementation.

If you have any other core scenarios where it's important, let me know and I can try to focus on them sooner, rather than later ;)