MappedSubresource.AsSpan<T> length parameter

[Kharzette]

Length sort of implies that it might want a count of T for the size of the span, but the code is expecting byte size.

However I've been having a lot of trouble with dotnet 6 sizeof getting my struct sizes wrong, so maybe byte size is better?

If it sticks with byte size, maybe change the name of length to byteSize or sizeInBytes.

[amerkoleci]

Thanks,
This commit fixes this one: 38f091a