[clangd] Fix an assertion failure in NamedDecl::getName during the prepareRename

[hokein]

Summary

getName method required to be called on a simple-identifier NamedDecl,
otherwise it will trigger an assertion.

clang-tools-extra/clangd/refactor/Rename.cpp

const NamedDecl *lookupSiblingWithinEnclosingScope(ASTContext &Ctx,
   // The following helpers check corresponding AST nodes for variable
   // declarations with the name collision.
   auto CheckDeclStmt = [&](const DeclStmt *DS,
                            StringRef Name) -> const NamedDecl * {
     if (!DS)
       return nullptr;
     for (const auto &Child : DS->getDeclGroup())
       if (const auto *ND = dyn_cast<NamedDecl>(Child))
-        if (ND != &RenamedDecl && ND->getName() == Name)
+        if (ND != &RenamedDecl && ND->getDeclName().isIdentifier() &&
+            ND->getName() == Name)
           return ND;
     return nullptr;
   };
   auto CheckCompoundStmt = [&](const Stmt *S,
                                StringRef Name) -> const NamedDecl * {
     if (const auto *CS = dyn_cast_or_null<CompoundStmt>(S))
       for (const auto *Node : CS->children())
         if (const auto *Result = CheckDeclStmt(dyn_cast<DeclStmt>(Node), Name))

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

Case Cases[] = {
 
       {R"cpp(// FIXME we probably want to rename both overloads here,
              // but renaming currently assumes there's only a 
              // single canonical declaration.
         namespace ns { int foo(int); char foo(char); }
         using ns::^foo;
       )cpp",
        "there are multiple symbols at the given location", !HeaderFile},
+
+      {R"cpp(
+        void test() {
+          // no crash
+          using namespace std;
+          int [[V^ar]];
+        }
+      )cpp",
+        nullptr, !HeaderFile},
   };
 
   for (const auto& Case : Cases) {
     SCOPED_TRACE(Case.Code);
     Annotations T(Case.Code);
     TestTU TU = TestTU::withCode(T.code());
     TU.ExtraArgs.push_back("-fno-delayed-template-parsing");
     if (Case.IsHeaderFile) {