Add toDynamic conversion for LinearGradient (facebook#54040)

Summary:
Pull Request resolved: facebook#54040

Implement toDynamic conversion of the LinearGradient following the parse logic as described here: https://www.internalfb.com/code/fbsource/[5fa7eb2b733a]/xplat/js/react-native-github/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/style/LinearGradient.kt?lines=24-76

Changelog: [Internal]

Reviewed By: christophpurrer

Differential Revision: D83788005

fbshipit-source-id: 9114451b12e31ad86abde54dbe2c8819a304e777

Author: Nick Lefever

packages/react-native/ReactCommon/react/renderer/graphics/LinearGradient.h

@@ -18,20 +18,61 @@ namespace facebook::react {
 
 enum class GradientDirectionType { Angle, Keyword };
 
+inline std::string toString(
+    const GradientDirectionType& gradientDirectionType) {
+  switch (gradientDirectionType) {
+    case GradientDirectionType::Angle:
+      return "angle";
+    case GradientDirectionType::Keyword:
+      return "keyword";
+  }
+
+  return "";
+}
+
 enum class GradientKeyword {
   ToTopRight,
   ToBottomRight,
   ToTopLeft,
   ToBottomLeft,
 };
 
+inline std::string toString(const GradientKeyword& gradientKeyword) {
+  switch (gradientKeyword) {
+    case GradientKeyword::ToTopRight:
+      return "to top right";
+    case GradientKeyword::ToBottomRight:
+      return "to bottom right";
+    case GradientKeyword::ToTopLeft:
+      return "to top left";
+    case GradientKeyword::ToBottomLeft:
+      return "to bottom left";
+  }
+
+  return "";
+}
+
 struct GradientDirection {
   GradientDirectionType type;
   std::variant<Float, GradientKeyword> value;
 
   bool operator==(const GradientDirection& other) const {
     return type == other.type && value == other.value;
   }
+
+#ifdef RN_SERIALIZABLE_STATE
+  folly::dynamic toDynamic() const {
+    folly::dynamic result = folly::dynamic::object();
+    result["type"] = toString(type);
+
+    if (std::holds_alternative<Float>(value)) {
+      result["value"] = std::get<Float>(value);
+    } else if (std::holds_alternative<GradientKeyword>(value)) {
+      result["value"] = toString(std::get<GradientKeyword>(value));
+    }
+    return result;
+  }
+#endif
 };
 
 struct LinearGradient {
@@ -41,6 +82,21 @@ struct LinearGradient {
   bool operator==(const LinearGradient& other) const {
     return direction == other.direction && colorStops == other.colorStops;
   }
+
+#ifdef RN_SERIALIZABLE_STATE
+  folly::dynamic toDynamic() const {
+    folly::dynamic result = folly::dynamic::object();
+    result["type"] = "linear-gradient";
+    result["direction"] = direction.toDynamic();
+
+    folly::dynamic colorStopsArray = folly::dynamic::array();
+    for (const auto& colorStop : colorStops) {
+      colorStopsArray.push_back(colorStop.toDynamic());
+    }
+    result["colorStops"] = colorStopsArray;
+    return result;
+  }
+#endif
 };
 
 inline GradientKeyword parseGradientKeyword(const std::string& keyword) {