Replace .sln with .slnx XML-based solution format

Replaced the traditional Visual Studio .sln file with a new .slnx file using an XML-based format. The new solution file includes all projects and solution items, modernizing the solution structure and improving compatibility with alternative tooling and editors.

Author: ds5678

AssetRipper.NativeDialogs.sln

@@ -0,0 +1,14 @@
+<Solution>
+  <Folder Name="/Solution Items/">
+    <File Path=".editorconfig" />
+    <File Path=".github/dependabot.yml" />
+    <File Path=".github/workflows/publish.yml" />
+    <File Path=".gitignore" />
+    <File Path="Directory.Build.props" />
+    <File Path="LICENSE" />
+    <File Path="README.md" />
+  </Folder>
+  <Project Path="AssetRipper.NativeDialogs.Example/AssetRipper.NativeDialogs.Example.csproj" />
+  <Project Path="AssetRipper.NativeDialogs.WebApi/AssetRipper.NativeDialogs.WebApi.csproj" />
+  <Project Path="AssetRipper.NativeDialogs/AssetRipper.NativeDialogs.csproj" />
+</Solution>