Move node cloning to YGConfig

Summary:
@public

Encapsulates node cloning within `YGConfig`.
This is necessary for allowing for context-aware cloning functions, which will ultimately allow for removal of weak global JNI references.

Reviewed By: shergin

Differential Revision: D14132608

fbshipit-source-id: 0dec114c8e172b1e34a4b7fd146c43f13c151ade

tests/YGConfigTest.cpp

@@ -0,0 +1,60 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the LICENSE
+ * file in the root directory of this source tree.
+ */
+// @Generated by gentest/gentest.rb from gentest/fixtures/YGDisplayTest.html
+
+#include <gtest/gtest.h>
+#include <yoga/Yoga.h>
+#include <yoga/YGConfig.h>
+#include <yoga/YGNode.h>
+
+#include <functional>
+#include <memory>
+
+struct ConfigCloningTest : public ::testing::Test {
+  std::unique_ptr<YGConfig, std::function<void(YGConfig*)>> config;
+  void SetUp() override;
+  void TearDown() override;
+
+  static YGNode clonedNode;
+  static YGNodeRef cloneNode(YGNodeRef, YGNodeRef, int) {
+    return &clonedNode;
+  }
+  static YGNodeRef doNotClone(YGNodeRef, YGNodeRef, int) {
+    return nullptr;
+  }
+};
+
+TEST_F(ConfigCloningTest, uses_values_provided_by_cloning_callback) {
+  config->setCloneNodeCallback(cloneNode);
+
+  YGNode node{}, owner{};
+  auto clone = config->cloneNode(&node, &owner, 0);
+
+  ASSERT_EQ(clone, &clonedNode);
+}
+
+TEST_F(
+    ConfigCloningTest,
+    falls_back_to_regular_cloning_if_callback_returns_null) {
+  config->setCloneNodeCallback(doNotClone);
+
+  YGNode node{}, owner{};
+  auto clone = config->cloneNode(&node, &owner, 0);
+
+  ASSERT_NE(clone, nullptr);
+  YGNodeFree(clone);
+}
+
+void ConfigCloningTest::SetUp() {
+  config = {YGConfigNew(), YGConfigFree};
+}
+
+void ConfigCloningTest::TearDown() {
+  config.reset();
+}
+
+YGNode ConfigCloningTest::clonedNode = {};