Plotters: make virtual void PLOTTER::Arc() using arc angles protected.

Using arc angles to plot an arc is really error prone due to different
options between plotters, and angles defined in Kicad, using this version of
arc plotting from Kicad is no longer allowed in Kicad code.

include/plotters/plotter.h

@@ -223,13 +223,6 @@ public:
     virtual void Arc( const VECTOR2I& aCenter, const VECTOR2I& aStart, const VECTOR2I& aEnd,
                       FILL_T aFill, int aWidth, int aMaxError );
 
-    /**
-     * Generic fallback: arc rendered as a polyline.
-     */
-    virtual void Arc( const VECTOR2I& aCentre, const EDA_ANGLE& aStartAngle,
-                      const EDA_ANGLE& aEndAngle, int aRadius, FILL_T aFill,
-                      int aWidth = USE_DEFAULT_LINE_WIDTH );
-
     /**
      * Generic fallback: Cubic Bezier curve rendered as a polyline
      * In KiCad the bezier curves have 4 control points:
@@ -310,10 +303,6 @@ public:
     virtual void ThickSegment( const VECTOR2I& start, const VECTOR2I& end, int width,
                                OUTLINE_MODE tracemode, void* aData );
 
-    virtual void ThickArc( const VECTOR2I& aCentre, const EDA_ANGLE& StAngle,
-                           const EDA_ANGLE& EndAngle, int aRadius, int aWidth,
-                           OUTLINE_MODE aTraceMode, void* aData );
-
     virtual void ThickArc( const VECTOR2I& aCentre, const VECTOR2I& aStart,
                            const VECTOR2I& aEnd, int aWidth,
                            OUTLINE_MODE aTraceMode, void* aData );
@@ -526,6 +515,17 @@ public:
 
 
 protected:
+    /**
+     * Generic fallback: arc rendered as a polyline.
+     */
+    virtual void Arc( const VECTOR2I& aCentre, const EDA_ANGLE& aStartAngle,
+                      const EDA_ANGLE& aEndAngle, int aRadius, FILL_T aFill,
+                      int aWidth = USE_DEFAULT_LINE_WIDTH );
+
+    virtual void ThickArc( const VECTOR2I& aCentre, const EDA_ANGLE& StAngle,
+                           const EDA_ANGLE& EndAngle, int aRadius, int aWidth,
+                           OUTLINE_MODE aTraceMode, void* aData );
+
     // These are marker subcomponents
     /**
      * Plot a circle centered on the position. Building block for markers