feat: Add .slnx solution format metadata generation support (dotnet#10540)

* feat: add `.slnx` solution format (Requires .NET 9 or later)

* chore: fix ci error of plantuml test

Author: filzrev

Directory.Packages.props

@@ -25,6 +25,12 @@
     <PackageVersion Include="YamlDotNet" Version="15.3.0" />
   </ItemGroup>
 
+  <!-- .slnx solution format is supported Microsoft.Build 17.13.9 or later. -->
+  <ItemGroup>
+    <PackageVersion Include="Microsoft.Build" Version="[17.11.4]" Condition="'$(TargetFramework)' == 'net8.0'"/>
+    <PackageVersion Include="Microsoft.Build" Version="17.13.9"   Condition="'$(TargetFramework)' != 'net8.0'"/>
+  </ItemGroup>
+
   <ItemGroup>
     <PackageVersion Include="Microsoft.CodeAnalysis" Version="4.12.0" />
     <PackageVersion Include="Microsoft.CodeAnalysis.Common" Version="4.12.0" />

src/Docfx.Dotnet/Docfx.Dotnet.csproj

@@ -31,6 +31,7 @@
     <PackageReference Include="OneOf" />
     <PackageReference Include="OneOf.SourceGenerator" PrivateAssets="All" />
     <PackageReference Include="Markdig" />
+    <PackageReference Include="Microsoft.Build" />
     <PackageReference Include="Microsoft.CodeAnalysis" />
     <PackageReference Include="Microsoft.CodeAnalysis.Common" />
     <PackageReference Include="Microsoft.CodeAnalysis.VisualBasic" />

src/Docfx.Dotnet/FileInformation.cs

@@ -48,6 +48,14 @@ private static FileType GetFileType(string filePath)
             case ".sln":
             case ".slnf":
                 return FileType.Solution;
+
+            case ".slnx":
+#if NET9_0_OR_GREATER
+                return FileType.Solution;
+#else
+                return FileType.NotSupported;
+#endif
+
             case ".csproj":
             case ".vbproj":
                 return FileType.Project;