LibGfx: Make Gfx::Path const-correct internally (segment list)

Userland/Libraries/LibGfx/Path.cpp

@@ -291,7 +291,7 @@ void Path::segmentize_path()
             break;
         }
         case Segment::Type::QuadraticBezierCurveTo: {
-            auto control = static_cast<QuadraticBezierCurveSegment&>(segment).through();
+            auto control = static_cast<QuadraticBezierCurveSegment const&>(segment).through();
             Painter::for_each_line_segment_on_bezier_curve(control, cursor, segment.point(), [&](FloatPoint p0, FloatPoint p1) {
                 add_line(p0, p1);
             });
@@ -309,7 +309,7 @@ void Path::segmentize_path()
             break;
         }
         case Segment::Type::EllipticalArcTo: {
-            auto& arc = static_cast<EllipticalArcSegment&>(segment);
+            auto& arc = static_cast<EllipticalArcSegment const&>(segment);
             Painter::for_each_line_segment_on_elliptical_arc(cursor, arc.point(), arc.center(), arc.radii(), arc.x_axis_rotation(), arc.theta_1(), arc.theta_delta(), [&](FloatPoint p0, FloatPoint p1) {
                 add_line(p0, p1);
             });

Userland/Libraries/LibGfx/Path.h

@@ -218,7 +218,7 @@ public:
         float x;
     };
 
-    NonnullRefPtrVector<Segment> const& segments() const { return m_segments; }
+    NonnullRefPtrVector<Segment const> const& segments() const { return m_segments; }
     auto& split_lines() const
     {
         if (!m_split_lines.has_value()) {
@@ -268,7 +268,7 @@ private:
         m_segments.append(adopt_ref(*new T(forward<Args>(args)...)));
     }
 
-    NonnullRefPtrVector<Segment> m_segments {};
+    NonnullRefPtrVector<Segment const> m_segments {};
 
     Optional<Vector<SplitLineSegment>> m_split_lines {};
     Optional<Gfx::FloatRect> m_bounding_box;