Replaces the `FetchContent` mechanism with a vendored copy of `tl/expected.hpp` (v1.1.0). The header is placed in `CGAL/tl/expected.hpp` to avoid namespace pollution. This also removes the CMake module `CGAL_setup_tl-excepted.cmake`. ## Release Management * Affected package(s): Constrained_triangulation_3 * Issue(s) solved (if any): #9145 * License and copyright ownership: CC0 1.0 Universal (tl/expected.hpp)