[PROPOSAL] Add VectorX structs mirroring the System.Numerics Vectors

[ghost]

Numerics Vectors only support floats, we could re-create them for Doubles, ints and longs (and possibly other types?).
This would allow users to take advantage of vector instructions without having to do loads and saves themselves.

[john-h-k]

This seems a good idea, but I would keep explicit loads and stores because they have a cost

[ghost]

Agreed, the JIT probably optimizes this away with the built-in types but we can't count on it doing the same thing in this case (especially since we'd be explicitly calling the SSE/AVX Load/Store functions).

[john-h-k]

I can/will/might do these, but they would just be a storage type, with proper ctors, ToString/GetHashCode/IEquatable<T>. No maths on them