[Rgen] Mark 'Constructor' named methods as constructors in the transf…

…ormer.

The old bindings use that name to denote constructors, these methods in
the new API will be converted to actual constructors.

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

@@ -36,6 +36,12 @@ public ExportData? ExportMethodData {
 	/// True if the method was exported with the MarshalNativeExceptions flag allowing it to support native exceptions.
 	/// </summary>
 	public bool MarshalNativeExceptions => HasMarshalNativeExceptionsFlag;
+
+	const string constructorName = "Constructor";
+	/// <summary>
+	/// True if the method is considered to be a constructor in the old bindings.
+	/// </summary>
+	public bool IsConstructor => Name == constructorName;
 
 	public Method (string type,
 		string name,

tests/rgen/Microsoft.Macios.Transformer.Tests/DataModel/MethodTests.cs

@@ -16,6 +16,21 @@ namespace Microsoft.Macios.Transformer.Tests.DataModel;
 
 public class MethodTests : BaseTransformerTestClass {
 
+	[Theory]
+	[InlineData ("Hello", false)]
+	[InlineData ("Constructor", true)]
+	public void IsConstructorTests (string methodName, bool expectedResult)
+	{
+		var method = new Method (
+			type: "TestClass",
+			name: methodName,
+			returnType: ReturnTypeForVoid (),
+			symbolAvailability: new(),
+			attributes: new(),
+			parameters: []);
+		Assert.Equal (expectedResult, method.IsConstructor);
+	}
+
 	class TestDataTryCreate : IEnumerable<object []> {
 		public IEnumerator<object []> GetEnumerator ()
 		{