Introduce TypedefEntity

pkg/compiler/lib/src/resolution/resolution_strategy.dart

Index: pkg/compiler/lib/src/resolution/resolution_strategy.dart
diff --git a/pkg/compiler/lib/src/resolution/resolution_strategy.dart b/pkg/compiler/lib/src/resolution/resolution_strategy.dart
index fff581f574bbc8604248fc6f4f4f4eb6dfa0219b..8c92e0bd0a21341b3598416f1f33129ca47090a7 100644
--- a/pkg/compiler/lib/src/resolution/resolution_strategy.dart
+++ b/pkg/compiler/lib/src/resolution/resolution_strategy.dart
@@ -678,6 +678,11 @@ class _CompilerElementEnvironment implements ElementEnvironment {
     });
     return values;
   }
+
+  @override
+  ResolutionFunctionType getTypedefAlias(covariant TypedefElement typedef) {
+    return typedef.alias;
+  }
 }
 
 /// AST-based logic for processing annotations. These annotations are processed