fix(dotnet): unable to pass 2d-array of interfaces (#2763)

When a 2-dimensional array of interfaces was passed, the `InferType`
function failed to account for interfaces, and failed instead of
correctly returning the relevant type reference.

Fixes aws/aws-cdk#12587



---

By submitting this pull request, I confirm that my contribution is made under the terms of the [Apache 2.0 license].

[Apache 2.0 license]: https://www.apache.org/licenses/LICENSE-2.0

packages/@jsii/dotnet-runtime-test/test/Amazon.JSII.Runtime.IntegrationTests/ComplianceTests.cs

@@ -1512,5 +1512,18 @@ public override String Repeat(String word)
                 return word;
             }
         }
+
+        [Fact(DisplayName = Prefix + nameof(ArrayOfInterfaces))]
+        public void ArrayOfInterfaces()
+        {
+            var bells = new IBell[1][];
+            bells[0] = new IBell[1];
+            bells[0][0] = new Bell();
+
+            var allTypes = new AllTypes();
+            allTypes.AnyProperty = bells;
+
+            Assert.Equal(bells, allTypes.AnyProperty);
+        }
     }
 }

packages/@jsii/dotnet-runtime/src/Amazon.JSII.Runtime/Services/Converters/FrameworkToJsiiConverter.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
@@ -348,6 +348,12 @@ TypeReference InferType(IReferenceMap referenceMap, Type type)
                 return new TypeReference(enumAttribute.FullyQualifiedName);
             }
 
+            var interfaceAttribute = type.GetCustomAttribute<JsiiInterfaceAttribute>();
+            if (interfaceAttribute != null)
+            {
+                return new TypeReference(interfaceAttribute.FullyQualifiedName);
+            }
+
             var structAttribute = type.GetCustomAttribute<JsiiByValueAttribute>();
             if (structAttribute != null)
             {