Add XML Docs

[SkyeHoefling]

Description

Update all public APIs in FileOnQ.Imaging.Heif to have proper xml docs. Verify the docs show up using the NuGet package.

[SkyeHoefling]

@kenny-sellers I assigned this one to you, I would like us to add xml docs to all public facing APIs so it is easier to understand downstream when integrating with the library