Add Span-based overloads of IsPNG, IsGIF, IsJPG

[uwx]

Adds Span-based overloads of the extension methods in TypeDetectionExtensions. I haven't removed the existing byte[] methods as that would break binary compatibility and possibly source compatibility (not sure on the latter).

[MazeXP]

Would it be a performance impact when actually having the IsPNG(byte[]) extension call the Span based extension by just passing the byte[] as ROS? Just thinking about avoiding duplicate code.

[uwx]

Would it be a performance impact when actually having the IsPNG(byte[]) extension call the Span based extension by just passing the byte[] as ROS? Just thinking about avoiding duplicate code.

That can be done, if desired. There should be no performance impact; it would look the same jitted.

[Nihlus]

I would prefer that, yeah.

[uwx]

Done.

[MazeXP]

LGTM, thanks.