Add Minimum Variable Line Width setting

This is similar to min_bead_width really, but applies to normal walls rather than thin parts.

Contributes to issue CURA-7686.

resources/definitions/fdmprinter.def.json

@@ -1067,6 +1067,18 @@
                     "default_value": "inward_distributed",
                     "limit_to_extruder": "wall_0_extruder_nr"
                 },
+                "wall_transition_threshold":
+                {
+                    "label": "Minimum Variable Line Width",
+                    "description": "The smallest line width, as a factor of the normal line width, beyond which it will choose to use fewer, but wider lines to fill the available space. Reduce this threshold to use more, thinner lines. Increase to use fewer, wider lines.",
+                    "type": "float",
+                    "unit": "%",
+                    "default_value": 50,
+                    "minimum_value": "1",
+                    "minimum_value_warning": "min_bead_width / line_width * 100",
+                    "maximum_value_warning": "75",
+                    "maximum_value": "100"
+                },
                 "wall_transition_length":
                 {
                     "label": "Wall Transition Length",