LibGfx: Add IPC serialization for Path

The compositor IPC path needs to move vector paths without teaching Web
code about the path wire format. Declare the Path specialization on the
owning LibGfx type, then reuse the existing path byte serialization for
IPC encode and decode.

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

Libraries/LibGfx/Path.cpp

@@ -6,6 +6,8 @@
 
 #include <LibGfx/Path.h>
 #include <LibGfx/PathSkia.h>
+#include <LibIPC/Decoder.h>
+#include <LibIPC/Encoder.h>
 
 namespace Gfx {
 
@@ -24,3 +26,20 @@ NonnullOwnPtr<Gfx::PathImpl> PathImpl::create()
 PathImpl::~PathImpl() = default;
 
 }
+
+namespace IPC {
+
+template<>
+ErrorOr<void> encode(Encoder& encoder, Gfx::Path const& path)
+{
+    return encoder.encode(path.serialize_to_bytes());
+}
+
+template<>
+ErrorOr<Gfx::Path> decode(Decoder& decoder)
+{
+    auto path_data = TRY(decoder.decode<Vector<u8>>());
+    return Gfx::Path::from_serialized_bytes(path_data);
+}
+
+}

Libraries/LibGfx/Path.h

@@ -15,6 +15,7 @@
 #include <LibGfx/Point.h>
 #include <LibGfx/Rect.h>
 #include <LibGfx/WindingRule.h>
+#include <LibIPC/Forward.h>
 
 namespace Gfx {
 
@@ -140,3 +141,13 @@ private:
 };
 
 }
+
+namespace IPC {
+
+template<>
+ErrorOr<void> encode(Encoder&, Gfx::Path const&);
+
+template<>
+ErrorOr<Gfx::Path> decode(Decoder&);
+
+}