Support ImageSharp 3

[jamesgurung]

In the latest major release of ImageSharp, there are some breaking API changes. This causes compatibility issues if a project uses ImageSharp 3 alongside PdfSharpCore.

Minimal repro:

Project.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net7.0</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="PdfSharpCore" Version="1.3.47" />
    <PackageReference Include="SixLabors.ImageSharp" Version="3.0.0" />
  </ItemGroup>
</Project>

Program.cs

using PdfSharpCore.Drawing;
var image = XImage.FromFile("test.png");

Error

System.MissingMethodException: 'Method not found: 'SixLabors.ImageSharp.Image`1<!!0> SixLabors.ImageSharp.Image.Load(System.String, SixLabors.ImageSharp.Formats.IImageFormat ByRef)'.' at PdfSharpCore.Utils.ImageSharpImageSource`1.FromFileImpl(String path, Nullable`1 quality) at MigraDocCore.DocumentObjectModel.MigraDoc.DocumentObjectModel.Shapes.ImageSource.FromFile(String path, Nullable`1 quality) at PdfSharpCore.Drawing.XImage..ctor(String path) at PdfSharpCore.Drawing.XImage.FromFile(String path, PdfReadAccuracy accuracy) at PdfSharpCore.Drawing.XImage.FromFile(String path) at Program.<Main>$(String[] args) in Program.cs:line 2