Obsolete ImageFormat out params and return on Metadata

[tocsoft]

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Proposal

This goes along with the https://github.com/SixLabors/ImageSharp/discussions/2090 proposal so show the impact to the API.

Description

Obsoletes all the overloads of Image.Load that return on IImageFormat, removes all internal dependencies on those APIs, returns OrginalImageFormat on all images/identify call sites.

out IImageFormat overloads no depend on non out versions rather than the other way around.