[clangd] Unwrap type sugar in HeuristicResolver::resolveTypeToRecordDecl()

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Summary

Fixes https://github.com/clangd/clangd/issues/1663

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Make the approach more general

clang-tools-extra/clangd/HeuristicResolver.cpp

 };
 
 // Helper function for HeuristicResolver::resolveDependentMember()
 // which takes a possibly-dependent type `T` and heuristically
 // resolves it to a CXXRecordDecl in which we can try name lookup.
 CXXRecordDecl *resolveTypeToRecordDecl(const Type *T) {
   assert(T);
 
+  // Unwrap type sugar such as type aliases.
+  T = T->getCanonicalTypeInternal().getTypePtr();
+
   if (const auto *RT = T->getAs<RecordType>())
     return dyn_cast<CXXRecordDecl>(RT->getDecl());
 
   if (const auto *ICNT = T->getAs<InjectedClassNameType>())
     T = ICNT->getInjectedSpecializationType().getTypePtrOrNull();
   if (!T)
     return nullptr;
 

clang-tools-extra/clangd/unittests/FindTargetTests.cpp

Code = R"cpp(
         };
         template <typename T>
         void test() {
           Foo::k(T()).template [[convert]]<T>();
         }
       )cpp";
   EXPECT_DECLS("CXXDependentScopeMemberExpr",
                "template <typename T> T convert() const");
+
+  Code = R"cpp(
+        template <typename T>
+        struct Waldo {
+          void find();
+        };
+        template <typename T>
+        using Wally = Waldo<T>;
+        template <typename T>
+        void foo(Wally<T> w) {
+          w.[[find]]();
+        }
+  )cpp";
+  EXPECT_DECLS("CXXDependentScopeMemberExpr", "void find()");
 }
 
 TEST_F(TargetDeclTest, DependentTypes) {
   // Heuristic resolution of dependent type name
   Code = R"cpp(
         template <typename>
         struct A { struct B {}; };