[RGen] Add attributes to the accessor struct in the generator. (#22055)

Author: mandel-macaque

src/rgen/Microsoft.Macios.Transformer.Generator/Microsoft.Macios.Transformer.Generator/XamarinBindingAPIGenerator.cs

@@ -242,6 +242,7 @@ void GenerateCode (SourceProductionContext context, Compilation compilation,
 		var models = new (string Model, AttributeTargets[] Targets) [] {
 			("EnumMember", [AttributeTargets.Field]), 
 			("Parameter", [AttributeTargets.Parameter]),
+			("Accessor", [AttributeTargets.Property]),
 			("Property", [AttributeTargets.Property]),
 			("Method", [AttributeTargets.Method]),
 			("Binding", [AttributeTargets.Interface, AttributeTargets.Class, AttributeTargets.Enum, AttributeTargets.Struct]),

src/rgen/Microsoft.Macios.Transformer/DataModel/Accessor.Transformer.cs

@@ -8,4 +8,6 @@ namespace Microsoft.Macios.Generator.DataModel;
 readonly partial struct Accessor {
 
 	public ExportData? ExportPropertyData { get; init; }
+
+	public Accessor () { }
 }