gh-41229: planar_graphs generator: support minimum_connectivity=4
plantri supports `-pc4` since version 5.0 released on October 2, 2016
but the [`planar_graphs()`](https://doc.sagemath.org/html/en/reference/g
raphs/sage/graphs/graph_generators.html#sage.graphs.graph_generators.Gra
phGenerators.planar_graphs) generator incorrectly claimed that
`minimum_connectivity=4` was not supported. This pull request rectifies
that.
I also tried adding support for a more broad range of options to the
`triangulations()` generator but I found it difficult to deal with the
complex requirements between the various parameters. According to its
README, plantri supports the following options, but not all combinations
are allowed:
```
Planar triangulations
connectivity 1, 2, 3, 4 or 5
minimum degree 3, 4 or 5
eulerian with connectivity 3 or 4
Planar quadrangulations
arbitrary simple
3-connected
minimum degree 3 and simple
3-connected, no non-facial 4-cycles
arbitrary
Planar simple graphs
connectivity 1, 2, 3 or 4
minimum degree 1, 2, 3, 4 or 5
Planar simple bipartite graphs
connectivity 1, 2 or 3
minimum degree 1, 2, or 3
Triangulations of a disk
connectivity 2 or 3
minimum degree 2 or 3
Planar cubic graphs
connectivity 1, 2, or 3
connectivity 1, 2, or 3
girth 3, 4 or 5
cyclic connectivity 3, 4 or 5
bipartite with cyclic connectivity 3 or 4
Planar quartic graphs
3-connected simple
4-edge-connected simple
4-edge-connected
3-connected, 6-cyclically-edge-connected
arbitrary
```
URL: https://github.com/sagemath/sage/pull/41229
Reported by: Lennard Hofmann
Reviewer(s):
