Plotters (especially DXF) add more precision when plotting arcs (and others)

- in DXF coordinates were using 6 digits for coordinate mantissa: this is not
enough for coord in inches. Now use 16 digits
- Arc( VECTOR2I& aCentre, EDA_ANGLE& aStartAngle, EDA_ANGLE& aEndAngle, ...)
was using integers for coord. This creates significant errors for start point
and end points of the arc. Now the center is given in double, and its position
is calculated from angle end points (and radius) to do not generate a position error
for these end points (previously the error could be 20 ... 50 nm)
Fixes #15056
https://gitlab.com/kicad/code/kicad/-/issues/15056

common/plotters/GERBER_plotter.cpp

@@ -817,8 +817,8 @@ void GERBER_PLOTTER::Circle( const VECTOR2I& aCenter, int aDiameter, FILL_T aFil
 
 
 
-void GERBER_PLOTTER::Arc( const VECTOR2I& aCenter, const EDA_ANGLE& aStartAngle,
-                          const EDA_ANGLE& aEndAngle, int aRadius, FILL_T aFill, int aWidth )
+void GERBER_PLOTTER::Arc( const VECTOR2D& aCenter, const EDA_ANGLE& aStartAngle,
+                          const EDA_ANGLE& aEndAngle, double aRadius, FILL_T aFill, int aWidth )
 {
     SetCurrentLineWidth( aWidth );
 
@@ -1140,8 +1140,8 @@ void GERBER_PLOTTER::ThickSegment( const VECTOR2I& start, const VECTOR2I& end, i
     }
 }
 
-void GERBER_PLOTTER::ThickArc( const VECTOR2I& aCentre, const EDA_ANGLE& aStartAngle,
-                               const EDA_ANGLE& aEndAngle, int aRadius, int aWidth,
+void GERBER_PLOTTER::ThickArc( const VECTOR2D& aCentre, const EDA_ANGLE& aStartAngle,
+                               const EDA_ANGLE& aEndAngle, double aRadius, int aWidth,
                                OUTLINE_MODE aTraceMode, void* aData )
 {
     GBR_METADATA *gbr_metadata = static_cast<GBR_METADATA*>( aData );