Fix Fabric umbrella search paths (#58622)

Summary:

Source-built CocoaPods frameworks do not automatically expose the source directories behind stable <React/...> umbrella includes. React-FabricComponents exports modal and text headers that consume umbrellas owned by React-Fabric, React-debug, React-rendererdebug, and React-utils, causing dynamic-framework builds to fail while resolving headers such as <React/RendererCore.h>.

Add the five owning source directories to React-FabricComponents HEADER_SEARCH_PATHS when frameworks and source-built RNCore are used. Keep prebuilt RNCore unchanged so its <React/...> headers continue to resolve from the prebuilt React.framework.

Changelog: [Internal]

Differential Revision: D120992289

Author: coado

packages/react-native/ReactCommon/React-FabricComponents.podspec

@@ -33,6 +33,17 @@ if ENV['USE_FRAMEWORKS']
     "\"$(PODS_TARGET_SRCROOT)/react/renderer/components/text/platform/cxx\"",
     "\"$(PODS_TARGET_SRCROOT)/react/renderer/components/view/platform/cxx\"",
   ]
+
+  if ReactNativeCoreUtils.build_rncore_from_source()
+    # Stable umbrellas consumed by exported component headers.
+    header_search_path = header_search_path + [
+      "\"$(PODS_TARGET_SRCROOT)/react/debug\"",
+      "\"$(PODS_TARGET_SRCROOT)/react/renderer/components/view\"",
+      "\"$(PODS_TARGET_SRCROOT)/react/renderer/core\"",
+      "\"$(PODS_TARGET_SRCROOT)/react/renderer/debug\"",
+      "\"$(PODS_TARGET_SRCROOT)/react/utils\"",
+    ]
+  end
 end
 
 Pod::Spec.new do |s|