Edge insertion for CMap/GMap (#7409)

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## Summary of Changes

Added the function `insert_cell_1_between_two_cells_2()` into
`GenericMap` concept, which allows users to insert an edge between two
different faces allowing to create faces with holes.

## Release Management

* Affected package(s): CMap/GMap
* Feature/Small Feature (if any):
https://cgal.geometryfactory.com/CGAL/Members/wiki/Features/Small_Features/Insert_edge_CMap/GMap
* Link to compiled documentation (obligatory for small feature) [*wrong
link name to be changed*](httpssss://wrong_URL_to_be_changed/Manual/Pkg)
* License and copyright ownership:

Combinatorial_map/doc/Combinatorial_map/Combinatorial_map.txt

@@ -168,7 +168,7 @@ Considering these different advantages and drawbacks, you can choose to use gene
 
 The diagram in \cgalFigureRef{fig_cmap_diagramme_class} shows the different classes of the package. `Combinatorial_map` is the main class (see Section \ref sseccombinatorialmap "Combinatorial Maps"). It allows to manage darts and attributes (see Section \ref ssecattributes "Cell Attributes"). Users can customize a combinatorial map thanks to an items class (see Section \ref ssecitem "Combinatorial Map Items"), which defines the information associated with darts and the attribute types. These types may be different for different dimensions, and they may also be void (note that the main concepts of `GenericMap`, `GenericMapItems` and `CellAttribute` are shared between combinatorial maps and generalized maps).
 
-The darts and attributes are accessed through <I>descriptors</I> (either Indices or Handles). A handle is a model of the `Handle` concept, thus supporting the two dereference operators `operator*` and `operator->`. All handles are model of `LessThanComparable` and `Hashable`, that is they can be used as keys in containers such as `std::map` and `std::unordered_map`. An index is a model of the `Index` concept, which is mainly an integer which is convertible from and to std::size_t. Indices can be used as index into vectors which store properties (cf. one example in Section \ref ssecexample3DCMWI "3D Combinatorial Map using Indices").
+The darts and attributes are accessed through <I>descriptors</I> (either Indices or Handles). A handle is a model of the `Handle` concept, thus supporting the two dereference operators `operator*` and `operator->`. All handles are model of `LessThanComparable` and `Hashable`, that is they can be used as keys in containers such as `std::map` and `std::unordered_map`. An index is a model of the `Index` concept, which is mainly an integer which is convertible from and to std::size_t. Indices can be used as index into vectors which store properties (cf. one example in Section \ref ssecexample3DCMWI "3D Combinatorial Map Using Indices").
 
 \cgalFigureBegin{fig_cmap_diagramme_class,cmap_diagramme_class.svg}
 UML diagram of the main classes of the package. k is the number of non void attributes.
@@ -393,6 +393,8 @@ Example of \link GenericMap::insert_cell_1_in_cell_2 `insert_cell_1_in_cell_2`\e
 
 `cm.`\link GenericMap::insert_dangling_cell_1_in_cell_2 `insert_dangling_cell_1_in_cell_2(d0)`\endlink adds a 1-cell in the 2-cell containing dart `d0`, the 1-cell being attached by only one of its vertex to the 0-cell containing dart `d0`.  This operation is possible if `d0`\f$ \in \f$ \link GenericMap::darts `cm.darts()`\endlink.
 
+`cm.`\link GenericMap::insert_cell_1_between_two_cells_2 `insert_cell_1_between_two_cells_2(d1,d2)`\endlink adds a 1-cell between the two faces containing containing darts `d1` and `d2`, between the two 0-cells containing darts `d1` and `d2`. The 2-cells are merged in one. This operation is possible if <I>d1</I>\f$ \not \in \f$ \f$ \langle{}\f$\f$ \beta_1\f$\f$ \rangle{}\f$(<I>d2</I>) which can be tested thanks to `cm.`\link GenericMap::is_insertable_cell_1_between_two_cells_2 `is_insertable_cell_1_between_two_cells_2(d1,d2)`\endlink.
+
 `cm.`\link GenericMap::insert_cell_2_in_cell_3 `insert_cell_2_in_cell_3(itbegin,itend)`\endlink adds a 2-cell in the 3-cell containing all the darts between `itbegin` and `itend`, along the path of 1-cells containing darts in [`itbegin`,`itend`). The 3-cell is split in two. This operation is possible if all the  darts in [`itbegin`,`itend`) form a closed path inside a same 3-cell  which can be tested thanks to `cm.`\link GenericMap::is_insertable_cell_2_in_cell_3 `is_insertable_cell_2_in_cell_3(itbegin,itend)`\endlink (see example on \cgalFigureRef{fig_cmap_insert_facet}).
 
 \cgalFigureBegin{fig_cmap_insert_facet,cmap_insert_facet.svg}
@@ -456,6 +458,24 @@ The second line is the result after the removal operations. We retrieve the orig
 Example of high level operations. Left: Initial 3D combinatorial map after the creation of the combinatorial hexahedron. Middle: Combinatorial map obtained after the two 1-cell insertions. The two 2-cells were split in two. Right: Combinatorial map obtained after the 2-cell insertion. The 3-cell was split in two.
 \cgalFigureEnd
 
+\subsection Combinatorial_mapInsertion Insert an Edge Between Two Different Faces
+
+\anchor ssecexempleinsertion
+
+This example shows the use of \link GenericMap::insert_cell_1_between_two_cells_2 `insert_cell_1_between_two_cells_2`\endlink operation. First we create a combinatorial hexahedron and a face with 4 edges. This face is inserted in the face of the hexahedron containing dart d1. We display the characteristics of the combinatorial map and check its validity. Then we count and display the number of 2-free darts.
+
+\cgalExample{Combinatorial_map/map_3_insert.cpp}
+
+The output is:
+\verbatim
+#Darts=30, #0-cells=12, #1-cells=17, #2-cells=6, #3-cells=1, #ccs=1, valid=1
+Number of 2-free darts: 4
+\endverbatim
+
+We can verify that there are 6 2-cells after the insertion since the squared face was inserted as a hole in one face of the hexahedron. We can also see that there are 4 2-free darts, which are the darts of the squared face. Since they bound an hole, there is no face filling the hole and thus 4 darts are 2-free.
+
+See also a similar example for Linear cell complex \ref Linear_cell_complexInsert "Insert an Edge Between Two Different Faces".
+
 \subsection Combinatorial_mapA4DGenericMap A 4D Combinatorial Map
 
 In this example, a 4-dimensional combinatorial map is used. Two tetrahedral cells are created and sewn by \f$ \beta_4\f$. Then the numbers of cells of the combinatorial map are displayed, and its validity is checked.
@@ -502,7 +522,7 @@ Lastly we remove the dynamic onmerge functor (step 7). This is done by initializ
 
 \cgalExample{Combinatorial_map/map_3_dynamic_onmerge.cpp}
 
-\subsection ssecexample3DCMWI 3D Combinatorial Map using Indices
+\subsection ssecexample3DCMWI 3D Combinatorial Map Using Indices
 
 In this example, a 3-dimensional combinatorial map is used, but using indices instead of handles. Two vectors are created to store some external information associated with darts and 3-attributes. Since descriptors are indices, they can directly be used to access elements of the vector.