ENH: add arachne engine for narrow internal solid infill

ConcentricGapFill pattern was used for internal narrow
solid infill. Use arachne engine instead to remove
gap fill inside the pattern and improve the extrusion path

Signed-off-by: salt.wei <salt.wei@bambulab.com>
Change-Id: I758d7c72eb71cc37026b7cebf746cc345014c3f5
(cherry picked from commit 0b6bacd21a091afc13d7b36a69e5b10f155bc6f8)

src/libslic3r/PrintConfig.cpp

@@ -482,7 +482,7 @@ void PrintConfigDef::init_fff_params()
     def->tooltip = L("Decrease this value slightly(for example 0.9) to reduce the amount of material for bridge, "
                      "to improve sag");
     def->min = 0;
-    def->max = 1;
+    def->max = 2.0;
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionFloat(1));