[generator] Fix reporting BI1042. (#13587)

Fix reporting BI1042 to include the type + property that triggered the error +
add a test.

src/generator.cs

@@ -6385,7 +6385,7 @@ public partial class Generator : IMemberGatherer {
 			}
 		} else if (BindThirdPartyLibrary) {
 			// User should provide a LibraryName
-			throw new BindingException (1042, true);
+			throw ErrorHelper.CreateError (1042, /* Missing '[Field (LibraryName=value)]' for {0} (e.g."__Internal") */ type.FullName + "." + propertyName);
 		} else {
 			library_name = type.Namespace;
 		}

tests/generator/ErrorTests.cs

@@ -129,6 +129,18 @@ namespace GeneratorTests
 			bgen.AssertErrorPattern (1041, "The selector doit:with:more: on type Derived is found multiple times with different argument types on argument 2 - System.Int32 : .*Foundation.NSObject.");
 		}
 
+		[Test]
+		public void BI1042 ()
+		{
+			var bgen = new BGenTool ();
+			bgen.Profile = Profile.iOS;
+			bgen.AddTestApiDefinition ("bi1042.cs");
+			bgen.CreateTemporaryBinding ();
+			bgen.ProcessEnums = true;
+			bgen.AssertExecuteError ("build");
+			bgen.AssertError (1042, "Missing '[Field (LibraryName=value)]' for BindingTests.Tools.DoorOpener (e.g.\"__Internal\")");
+		}
+
 		[Test]
 		public void BI1046 ()
 		{

tests/generator/bi1042.cs

@@ -0,0 +1,10 @@
+using System;
+using Foundation;
+
+namespace BindingTests
+{
+	public enum Tools {
+		[Field ("DoorOpener")]
+		DoorOpener,
+	}
+}