Refactor ParagraphComponentDescriptor to support subclassing (facebook#55634)

Summary:

Extract ParagraphComponentDescriptor logic into a template base class BaseParagraphComponentDescriptor<ShadowNodeT> so that other paragraph-like component descriptors can reuse the same TextLayoutManager wiring. Remove `final` from ParagraphShadowNode to allow subclassing. Move TextLayoutManagerKey from extern linkage in .cpp to constexpr in the new header.

This is a pure refactor with no behavioral change.

Changelog:
[Internal]

Reviewed By: cortinico

Differential Revision: D93829402

Author: NickGerleman

packages/react-native/ReactCommon/react/renderer/components/text/BaseParagraphComponentDescriptor.h

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <react/renderer/core/ConcreteComponentDescriptor.h>
+#include <react/renderer/textlayoutmanager/TextLayoutManager.h>
+#include <react/utils/ContextContainer.h>
+
+namespace facebook::react {
+
+constexpr const char *const TextLayoutManagerKey = "TextLayoutManager";
+
+template <typename ShadowNodeT>
+class BaseParagraphComponentDescriptor : public ConcreteComponentDescriptor<ShadowNodeT> {
+ public:
+  explicit BaseParagraphComponentDescriptor(const ComponentDescriptorParameters &parameters)
+      : ConcreteComponentDescriptor<ShadowNodeT>(parameters),
+        textLayoutManager_(getManagerByName<TextLayoutManager>(this->contextContainer_, TextLayoutManagerKey))
+  {
+  }
+
+  ComponentName getComponentName() const override
+  {
+    return ShadowNodeT::Name();
+  }
+
+ protected:
+  void adopt(ShadowNode &shadowNode) const override
+  {
+    ConcreteComponentDescriptor<ShadowNodeT>::adopt(shadowNode);
+
+    auto &paragraphShadowNode = static_cast<ShadowNodeT &>(shadowNode);
+
+    // `ParagraphShadowNode` uses `TextLayoutManager` to measure text content
+    // and communicate text rendering metrics to mounting layer.
+    paragraphShadowNode.setTextLayoutManager(textLayoutManager_);
+  }
+
+ private:
+  // Every `ParagraphShadowNode` has a reference to a shared `TextLayoutManager`
+  const std::shared_ptr<const TextLayoutManager> textLayoutManager_;
+};
+
+} // namespace facebook::react

packages/react-native/ReactCommon/react/renderer/components/text/ParagraphComponentDescriptor.cpp

@@ -7,41 +7,16 @@
 
 #pragma once
 
+#include <react/renderer/components/text/BaseParagraphComponentDescriptor.h>
 #include <react/renderer/components/text/ParagraphShadowNode.h>
-#include <react/renderer/core/ConcreteComponentDescriptor.h>
-#include <react/renderer/textlayoutmanager/TextLayoutManager.h>
-#include <react/utils/ContextContainer.h>
 
 namespace facebook::react {
-
-extern const char TextLayoutManagerKey[];
-
 /*
  * Descriptor for <Paragraph> component.
  */
-class ParagraphComponentDescriptor final : public ConcreteComponentDescriptor<ParagraphShadowNode> {
+class ParagraphComponentDescriptor final : public BaseParagraphComponentDescriptor<ParagraphShadowNode> {
  public:
-  explicit ParagraphComponentDescriptor(const ComponentDescriptorParameters &parameters)
-      : ConcreteComponentDescriptor<ParagraphShadowNode>(parameters),
-        textLayoutManager_(getManagerByName<TextLayoutManager>(contextContainer_, TextLayoutManagerKey))
-  {
-  }
-
- protected:
-  void adopt(ShadowNode &shadowNode) const override
-  {
-    ConcreteComponentDescriptor::adopt(shadowNode);
-
-    auto &paragraphShadowNode = static_cast<ParagraphShadowNode &>(shadowNode);
-
-    // `ParagraphShadowNode` uses `TextLayoutManager` to measure text content
-    // and communicate text rendering metrics to mounting layer.
-    paragraphShadowNode.setTextLayoutManager(textLayoutManager_);
-  }
-
- private:
-  // Every `ParagraphShadowNode` has a reference to a shared `TextLayoutManager`
-  const std::shared_ptr<const TextLayoutManager> textLayoutManager_;
+  using BaseParagraphComponentDescriptor::BaseParagraphComponentDescriptor;
 };
 
 } // namespace facebook::react

packages/react-native/ReactCommon/react/renderer/components/text/ParagraphComponentDescriptor.h

@@ -26,7 +26,7 @@ extern const char ParagraphComponentName[];
  * containing and displaying text. Text content is represented as nested <Text>
  * and <RawText> components.
  */
-class ParagraphShadowNode final
+class ParagraphShadowNode
     : public ConcreteViewShadowNode<ParagraphComponentName, ParagraphProps, ParagraphEventEmitter, ParagraphState>,
       public BaseTextShadowNode {
  public: