LibGfx: Add IPC serialization for CornerRadii

The compositor IPC boundary needs to transfer CSS corner radii without
keeping their wire shape in Web-specific glue. Declare the IPC
specializations on the LibGfx types and encode each corner radius pair
next to the CornerRadii implementation.

This is preparatory work required to add IPC between the main and
compositor threads.

Libraries/LibGfx/CornerRadii.cpp

@@ -7,6 +7,8 @@
 
 #include <AK/Math.h>
 #include <LibGfx/CornerRadii.h>
+#include <LibIPC/Decoder.h>
+#include <LibIPC/Encoder.h>
 
 namespace Gfx {
 
@@ -44,3 +46,45 @@ void CornerRadii::adjust_corners_for_spread_distance(int spread_distance)
 }
 
 }
+
+namespace IPC {
+
+template<>
+ErrorOr<void> encode(Encoder& encoder, Gfx::CornerRadius const& radius)
+{
+    TRY(encoder.encode(radius.horizontal_radius));
+    TRY(encoder.encode(radius.vertical_radius));
+    return {};
+}
+
+template<>
+ErrorOr<Gfx::CornerRadius> decode(Decoder& decoder)
+{
+    return Gfx::CornerRadius {
+        .horizontal_radius = TRY(decoder.decode<int>()),
+        .vertical_radius = TRY(decoder.decode<int>()),
+    };
+}
+
+template<>
+ErrorOr<void> encode(Encoder& encoder, Gfx::CornerRadii const& radii)
+{
+    TRY(encoder.encode(radii.top_left));
+    TRY(encoder.encode(radii.top_right));
+    TRY(encoder.encode(radii.bottom_right));
+    TRY(encoder.encode(radii.bottom_left));
+    return {};
+}
+
+template<>
+ErrorOr<Gfx::CornerRadii> decode(Decoder& decoder)
+{
+    return Gfx::CornerRadii {
+        .top_left = TRY(decoder.decode<Gfx::CornerRadius>()),
+        .top_right = TRY(decoder.decode<Gfx::CornerRadius>()),
+        .bottom_right = TRY(decoder.decode<Gfx::CornerRadius>()),
+        .bottom_left = TRY(decoder.decode<Gfx::CornerRadius>()),
+    };
+}
+
+}

Libraries/LibGfx/CornerRadii.h

@@ -9,6 +9,7 @@
 
 #include <LibGfx/Point.h>
 #include <LibGfx/Rect.h>
+#include <LibIPC/Forward.h>
 
 namespace Gfx {
 
@@ -90,3 +91,19 @@ struct CornerRadii {
 };
 
 }
+
+namespace IPC {
+
+template<>
+ErrorOr<void> encode(Encoder&, Gfx::CornerRadius const&);
+
+template<>
+ErrorOr<Gfx::CornerRadius> decode(Decoder&);
+
+template<>
+ErrorOr<void> encode(Encoder&, Gfx::CornerRadii const&);
+
+template<>
+ErrorOr<Gfx::CornerRadii> decode(Decoder&);
+
+}