Summary: Fix DanglingHandleCheck to match conversion operator whose return type is a type alias, e.g. `std::string`'s conversion operator to `std::string_view`.

clang-tools-extra/clang-tidy/bugprone/DanglingHandleCheck.cpp

 namespace {
 
 ast_matchers::internal::BindableMatcher<Stmt>
 handleFrom(const ast_matchers::internal::Matcher<RecordDecl> &IsAHandle,
            const ast_matchers::internal::Matcher<Expr> &Arg) {
   return expr(
       anyOf(cxxConstructExpr(hasDeclaration(cxxMethodDecl(ofClass(IsAHandle))),
                              hasArgument(0, Arg)),
-            cxxMemberCallExpr(hasType(cxxRecordDecl(IsAHandle)),
+            cxxMemberCallExpr(hasType(hasUnqualifiedDesugaredType(recordType(
+                                  hasDeclaration(cxxRecordDecl(IsAHandle))))),
                               callee(memberExpr(member(cxxConversionDecl()))),
                               on(Arg))));
 }
 
 ast_matchers::internal::Matcher<Stmt> handleFromTemporaryValue(
     const ast_matchers::internal::Matcher<RecordDecl> &IsAHandle) {
   // If a ternary operator returns a temporary value, then both branches hold a
   // temporary value. If one of them is not a temporary then it must be copied

clang-tools-extra/test/clang-tidy/checkers/bugprone-dangling-handle.cpp

 template <typename Key, typename Value>
 class map {
  public:
   using value_type = pair<Key, Value>;
   value_type& operator[](const Key& key);
   value_type& operator[](Key&& key);
 };
 
+template <typename _CharT>
 class basic_string_view;
 
+template <typename _CharT>
 class basic_string {
- public:
+  typedef basic_string_view<_CharT> __self_view;
   basic_string();
   basic_string(const char*);
 
-  operator basic_string_view() const noexcept;
+  operator __self_view() const noexcept;
 
   ~basic_string();
 };
 
-typedef basic_string string;
+typedef basic_string<char> string;
 
+template <typename _CharT>
 class basic_string_view {
- public:
   basic_string_view(const char*);
 };
 
-typedef basic_string_view string_view;
+typedef basic_string_view<char> string_view;
 
 }  // namespace std
 
 namespace llvm {
 
 class StringRef {
  public:
   StringRef();