fix: TypeReference support

Author: NeedleInAJayStack

Sources/GraphQL/Execution/Execute.swift

@@ -969,6 +969,21 @@ func completeValue(
                 )
             }
 
+            // If field type is a TypeReference, find the type itself.
+            if
+                let returnType = returnType as? GraphQLTypeReference,
+                let referencedType = info.schema.typeMap[returnType.name]
+            {
+                return try completeValue(
+                    exeContext: exeContext,
+                    returnType: referencedType,
+                    fieldASTs: fieldASTs,
+                    info: info,
+                    path: path,
+                    result: .success(exeContext.eventLoopGroup.any().makeSucceededFuture(result))
+                )
+            }
+
             // Not reachable. All possible output types have been considered.
             throw GraphQLError(
                 message: "Cannot complete value of unexpected type \"\(returnType)\"."

Sources/GraphQL/Execution/Values.swift

@@ -88,9 +88,16 @@ func getVariableValue(
     definitionAST: VariableDefinition,
     input: Map
 ) throws -> Map {
-    let type = typeFromAST(schema: schema, inputTypeAST: definitionAST.type)
+    var type = typeFromAST(schema: schema, inputTypeAST: definitionAST.type)
     let variable = definitionAST.variable
 
+    if let typeReference = type as? GraphQLTypeReference {
+        guard let referencedType = schema.typeMap[typeReference.name] else {
+            throw GraphQLError(message: "Referenced type \(typeReference.name) not found")
+        }
+        type = referencedType
+    }
+
     guard let inputType = type as? GraphQLInputType else {
         throw GraphQLError(
             message: