Adds a scale_gizmo_handles entry to the Touchscreen editor settings

When enabled, this scales the editor icons to improve usability on touchscreen devices.
In addition this commit fixes touch detection for the collision_shape_2d_editor_plugin so it scales with the icons size.

editor/plugins/curve_editor_plugin.h

@@ -117,6 +117,7 @@ private:
 	// Constant
 	float _hover_radius;
 	float _tangents_length;
+	float _gizmo_handle_scale = 1.0;
 };
 
 class EditorInspectorPluginCurve : public EditorInspectorPlugin {