LibGfx: Fix dynamic_cast undefined behavior on macOS

MacOS XCode 16 breaks dynamic_cast on final classes where the base
class has a has a virtual destructor defined in the header, which
creates a different virtual table per translation unit.
This is probably a regression in Apple's Clang that causes final
classes to be incorrectly aggressively optimized.
https://stackoverflow.com/questions/79192304/macos-xcode-16-breaks-dynamic-cast-for-final-types-defined-in-shared-library

Libraries/LibGfx/PaintStyle.h

@@ -38,7 +38,7 @@ class PaintStyle : public RefCounted<PaintStyle> {
     virtual Color sample_color(IntPoint) const { return Color(); }
 };
 
-class SolidColorPaintStyle final : public PaintStyle {
+class SolidColorPaintStyle : public PaintStyle {
 public:
     static ErrorOr<NonnullRefPtr<SolidColorPaintStyle>> create(Color color)
     {
@@ -90,7 +90,7 @@ class GradientPaintStyle : public PaintStyle {
 // These gradients are (unlike CSS ones) not relative to the painted shape, and do not
 // support premultiplied alpha.
 
-class CanvasLinearGradientPaintStyle final : public GradientPaintStyle {
+class CanvasLinearGradientPaintStyle : public GradientPaintStyle {
 public:
     static ErrorOr<NonnullRefPtr<CanvasLinearGradientPaintStyle>> create(FloatPoint p0, FloatPoint p1)
     {
@@ -113,7 +113,7 @@ class CanvasLinearGradientPaintStyle final : public GradientPaintStyle {
     FloatPoint m_p1;
 };
 
-class CanvasConicGradientPaintStyle final : public GradientPaintStyle {
+class CanvasConicGradientPaintStyle : public GradientPaintStyle {
 public:
     static ErrorOr<NonnullRefPtr<CanvasConicGradientPaintStyle>> create(FloatPoint center, float start_angle = 0.0f)
     {
@@ -133,7 +133,7 @@ class CanvasConicGradientPaintStyle final : public GradientPaintStyle {
     float m_start_angle { 0.0f };
 };
 
-class CanvasRadialGradientPaintStyle final : public GradientPaintStyle {
+class CanvasRadialGradientPaintStyle : public GradientPaintStyle {
 public:
     static ErrorOr<NonnullRefPtr<CanvasRadialGradientPaintStyle>> create(FloatPoint start_center, float start_radius, FloatPoint end_center, float end_radius)
     {
@@ -190,7 +190,7 @@ class SVGGradientPaintStyle : public GradientPaintStyle {
     SpreadMethod m_spread_method { SpreadMethod::Pad };
 };
 
-class SVGLinearGradientPaintStyle final : public SVGGradientPaintStyle {
+class SVGLinearGradientPaintStyle : public SVGGradientPaintStyle {
 public:
     static ErrorOr<NonnullRefPtr<SVGLinearGradientPaintStyle>> create(FloatPoint p0, FloatPoint p1)
     {