Add 2D honeycomb infill pattern (#9483)

* Add 2D honeycomb infill pattern

* Reverted change of 2D lattice infill void area estimation

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Co-authored-by: Noisyfox <timemanager.rick@gmail.com>

src/libslic3r/Layer.cpp

@@ -387,6 +387,7 @@ coordf_t Layer::get_sparse_infill_max_void_area()
             case ipAlignedRectilinear:
             case ipOctagramSpiral:
             case ipHilbertCurve:
+            case ip2DHoneycomb:
             case ip3DHoneycomb:
             case ipArchimedeanChords:
                 max_void_area = std::max(max_void_area, spacing * spacing);