Span<T> api update (#8583)

Span<T> api update (#8583)

* Changing method/property order to match CoreFX impl

To make diffing the files easier

* Added other missing methods to match CoreFX impl

Added:
- public void CopyTo(Span<T> destination)
- public static bool operator ==(Span<T> left, Span<T> right)
- public static bool operator !=(Span<T> left, Span<T> right)
- public override bool Equals(object obj)
- public override int GetHashCode()

Also removed 'public void Set(ReadOnlySpan<T> values)' and it's no
longer part of the Span<T> public API, see

https://github.com/dotnet/apireviews/tree/master/2016/11-04-SpanOfT#spantset