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)
Sebastien Loriot
93093e8dd4