Add support for embedding data in generated C++ code

This allows compiling with SIXTYFPS_EMBED_RESOURCES=true and
images/fonts are embedded as inline variables.

Generated data is emitted into the header file as

   inline uint8_t sfps_embedded_resources_123[789] = {
       0x1, 0x2, 0x3,
   };

api/sixtyfps-cpp/include/sixtyfps.h

@@ -863,7 +863,7 @@ auto blocking_invoke_from_event_loop(Functor f) -> std::invoke_result_t<Functor>
 namespace private_api {
 
 /// Registers a font by the specified path. The path must refer to an existing
-/// TrueType font font.
+/// TrueType font.
 /// \returns an empty optional on success, otherwise an error string
 inline std::optional<SharedString> register_font_from_path(const SharedString &path)
 {
@@ -876,6 +876,20 @@ inline std::optional<SharedString> register_font_from_path(const SharedString &p
     }
 }
 
+/// Registers a font by the data. The data must be valid TrueType font data.
+/// \returns an empty optional on success, otherwise an error string
+inline std::optional<SharedString> register_font_from_data(const uint8_t *data, std::size_t len)
+{
+    SharedString maybe_err;
+    cbindgen_private::sixtyfps_register_font_from_data({ const_cast<uint8_t *>(data), len },
+                                                       &maybe_err);
+    if (!maybe_err.empty()) {
+        return maybe_err;
+    } else {
+        return {};
+    }
+}
+
 }
 
 } // namespace sixtyfps

api/sixtyfps-cpp/include/sixtyfps_image.h

@@ -69,6 +69,9 @@ public:
     /// Returns false if \a a refers to the same image as \a b; true otherwise.
     friend bool operator!=(const Image &a, const Image &b) { return a.data != b.data; }
 
+    /// \private
+    explicit Image(cbindgen_private::types::Image inner) : data(inner) { }
+
 private:
     using Tag = cbindgen_private::types::ImageInner::Tag;
     using Data = cbindgen_private::types::Image;