ReadOnlySpan<byte> friendly overload for WriteFile

[jnm2]

(0.1.506-beta)

https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-writefile#parameters has void* lpBuffer, uint nNumberOfBytesToWrite. Since the second parameter explicitly defines the previous parameter in terms of bytes, it seems like the friendly overload could replace both parameters with ReadOnlySpan<byte> buffer.

The benefit would be avoiding adding unsafe + fixed around the call.

[AArnott]

Hmmmm... unless we special case it (and we try to minimize such cases), the most natural way to achieve this is to get the metadata to change from void* to byte*. If they were to do that, I believe you'd automatically get what you want. And with some other enhancements, the nNumberOfBytesToWrite would also disappear from the friendly overload because that value can come from the span's length.

Although strictly speaking, the current void* allows pointers to any other blittable structure, if that ever was useful to anyone they could do a typecast to make it look like byte* and proceed anyway.

So I'm in favor of this change. Moving to the metadata repo.

[AArnott]

The request for the metadata repo is to change the void* parameter to be byte* instead.