V12: Update ImageSharp V3 and Add Legacy V2 Project

[nikolajlauridsen]

This PR takes #14180 but instead of just upgrading the ImageSharp project to V3, it also adds the old V2 version as a separate project.

For more info see #14180

As for testing as also stated in the other PR, the tests should pass and you should be able to get a cropped image.

[Zeegaan]

LGTM 👍

[ronaldbarendse]

Just a note about naming of the projects/packages: I would suggest always including the major version of the dependency, e.g. Umbraco.Cms.Imaging.ImageSharp3 and Umbraco.Cms.Imaging.ImageSharp2 (using Umbraco.Cms.Imaging.ImageSharp.V2 could infer there might be a dependency on Umbraco.Cms.Imaging.ImageSharp, which isn't the case).

Besides being more clear on what major version the dependency is used, this will also be much better for future-proofing, especially if we'd like to support a future ImageSharp 4 dependency on our CMS v13 LTS version (which could then be released as Umbraco.Cms.Imaging.ImageSharp4 - nice, simple and most of all, logical).