Fixed an issue where the `record struct` type declared with a primary constructor could not be decompiled correctly. The reason was that `HandleInstanceFieldInitializers` did not support the `struct` type, but `DetectPrimaryConstructor` did not exclude it in advance.

Here's an example:
```cs
    public record struct CopilotContextId_RecordStruct(Guid id)
    {
        public Guid guid { get; } = id;

        public CopilotContextId_RecordStruct() : this(Guid.NewGuid())
        {

        }
    }
```

ICSharpCode.Decompiler/CSharp/RecordDecompiler.cs

@@ -210,6 +210,8 @@ namespace ICSharpCode.Decompiler.CSharp
 			{
 				if (!settings.UsePrimaryConstructorSyntax)
 					return null;
+				if (isStruct)
+					return null;
 			}
 			else
 			{