C++ std::variant::operator= page is empty

https://devdocs.io/cpp/utility/variant/operator=

Page is completely empty, but with correct footer and proper link to cppreference.com.
Other std::variant pages are fine.

Tested on online documentation, via Vivaldi and Edge.

Open the linked std::variant::operator= page and compare it with the other std::variant pages, checking the documentation source or generation path that produces the empty page. Done means the page renders its expected C++ documentation while retaining the existing footer and cppreference.com link.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.