## Summary of Changes
Important various fixes and improvements, from an experimental branch of
mine about CDT_3.
- <s>remove CMake warnings about `VTK_USE_FILE`</s> (our testsuite tests
with [VTK-8.2](https://docs.vtk.org/en/latest/release_details/8.2.html),
whereas
[VTK-9.0](https://docs.vtk.org/en/latest/release_details/9.0.html) was
released four years ago).
- make `Circulator_from_container` compatible with ranges (instead of
just containers)
- `Hash_map` is move-constructible and -assignable
- add preliminary support for C++20 concepts and `<format>`
- [x] add `Compare_angle_3(Point_3, Point_3, Point_3, Point_3, Point_3,
Point_3)` (with six points) **TODO: needs doc**... will be handled later
in issue #8219
- [x] **breaking changes:** add `Compare_xy_2` to
`TriangulationTraits_2` <s>TODO: needs announcement</s>
- fix `Compact_container` time stamp feature
- [x] commits from #7410 **That is probably a problem, to be fixed.**
**fixed in #7410 and then my the merge
70464ea107**
- add `CGAL::Scope_exit`, `CGAL::make_scope_exit`, for CGAL developers
(undocumented)
- add an overload of `make_sorted_pair` with only one pair-like argument
- improve `CGAL::IO::Output_ref` and `oformat`
- perf improvements in
`TDS_3/include/CGAL/Triangulation_data_structure_3.h` (`is_edge` is 7
times faster)
- <s>perf improvement in
`Triangulation_2/include/CGAL/Triangulation_2/internal/Polyline_constraint_hierarchy_2.h`
(with the use of `unordered_flat_map` from Boost>=1.80</s>
- less filter failures in `Triangulation_segment_cell_iterator_3`
- add `Triangulation_3::is_facet(u, v, w)` (without `, c, i, j, k`)
## Release Management
* Affected package(s): Installation, T_2, TDS_2, T_3, TDS_3, SMDS_3,
Kernel, STL_Extension, Stream_support
* Feature/Small Feature (if any):
* License and copyright ownership: maintenance by GeometryFactory
## Summary of Changes
Switching from `std::pair<Property_map<T>, bool>` to `std::optional` in
`Property_container::get<T>`
Introducing `Pair_optional_adaptor` for backward compatibility which
extends `std::optional<T>` to interface of `std::pair`
using `Pair_optional_adaptor` for `Surface_mesh` and `Point_set_3`
## Release Management
* Affected package(s): Point_set_3, Surface_mesh, STL_Extension
Laurent Rineau
Sébastien Loriot
albert-github
Sven Oesau
Jane Tournois
Andreas Fabri