import all shipped nuget packages as built-in

also would now throw if version gets changed

NuGet/Models/NuGetRuntimeFramework.cs

@@ -0,0 +1,27 @@
+using System.Text.Json.Serialization;
+using NuGet.Converters;
+using NuGet.Frameworks;
+
+namespace NuGet.Models;
+
+/// <summary>
+/// Represents a NuGetFramework with a runtime identifier
+/// </summary>
+[JsonConverter(typeof(RuntimeFrameworkJsonConverter))]
+public record NuGetRuntimeFramework(NuGetFramework Framework, string? RuntimeIdentifier)
+{
+    public static NuGetRuntimeFramework Parse(string str)
+    {
+        var index = str.IndexOf('/');
+        
+        if (index < 0)
+            return new NuGetRuntimeFramework(NuGetFramework.Parse(str), null);
+        
+        return new NuGetRuntimeFramework(NuGetFramework.Parse(str[..index]), str[(index + 1)..]);
+    }
+
+    public override string ToString()
+    {
+        return string.IsNullOrEmpty(RuntimeIdentifier) ? Framework.ToString() : $"{Framework}/{RuntimeIdentifier}";
+    }
+}