Generate RN specific Files in RN (#47458)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/47458

We are in a weird situation where React Native depends on some files that are generated by Codegen.

Codegen runs in the user project, so those dependencies are not available to React Native if we try to build it in isolation.

This is a problem and a blocker to prepare the prebuilds for iOS.

This image show the changes we are introducing:
On the right we have the current situation.
On the left the new one.

{F1954418630}

## Changelog:
[Internal] - Generate React Native specific code inside React Native

Reviewed By: cortinico, blakef

Differential Revision: D65541505

fbshipit-source-id: 1412d7f23c4d2230b795af41f1e832c8a70d5859

packages/react-native/React/React-RCTFBReactNativeSpec.podspec

@@ -0,0 +1,84 @@
+# 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.
+
+require "json"
+
+package = JSON.parse(File.read(File.join(__dir__, "..", "package.json")))
+version = package['version']
+
+source = { :git => 'https://github.com/facebook/react-native.git' }
+if version == '1000.0.0'
+  # This is an unpublished version, use the latest commit hash of the react-native repo, which we’re presumably in.
+  source[:commit] = `git rev-parse HEAD`.strip if system("git rev-parse --git-dir > /dev/null 2>&1")
+else
+  source[:tag] = "v#{version}"
+end
+
+module_name = "FBReactNativeSpec"
+header_dir = "FBReactNativeSpec"
+
+folly_config = get_folly_config()
+folly_compiler_flags = folly_config[:compiler_flags]
+folly_version = folly_config[:version]
+boost_config = get_boost_config()
+boost_compiler_flags = boost_config[:compiler_flags]
+new_arch_flags = ENV['RCT_NEW_ARCH_ENABLED'] == '1' ? ' -DRCT_NEW_ARCH_ENABLED=1' : ''
+
+header_search_paths = [
+  "\"$(PODS_ROOT)/RCT-Folly\"",
+]
+
+Pod::Spec.new do |s|
+  s.name                   = "React-RCTFBReactNativeSpec"
+  s.version                = version
+  s.summary                = "FBReactNativeSpec for React Native."
+  s.homepage               = "https://reactnative.dev/"
+  s.license                = package["license"]
+  s.author                 = "Meta Platforms, Inc. and its affiliates"
+  s.platforms              = min_supported_versions
+  s.source                 = source
+  s.source_files           = "FBReactNativeSpec/**/*.{c,h,m,mm,S,cpp}"
+  s.compiler_flags         = folly_compiler_flags + ' ' + boost_compiler_flags + new_arch_flags
+  s.header_dir             = header_dir
+  s.module_name            = module_name
+  s.pod_target_xcconfig    = {
+    "HEADER_SEARCH_PATHS" => header_search_paths,
+    "OTHER_CFLAGS" => "$(inherited) " + folly_compiler_flags + new_arch_flags,
+    "CLANG_CXX_LANGUAGE_STANDARD" => rct_cxx_language_standard()
+  }
+
+  s.dependency "React-jsi"
+  s.dependency "React-jsiexecutor"
+  s.dependency "RCT-Folly"
+  s.dependency "RCTRequired"
+  s.dependency "RCTTypeSafety"
+  s.dependency "React-Core"
+  s.dependency "React-NativeModulesApple"
+  add_dependency(s, "ReactCommon", :subspec => "turbomodule/core", :additional_framework_paths => ["react/nativemodule/core"])
+  add_dependency(s, "ReactCommon", :subspec => "turbomodule/bridging", :additional_framework_paths => ["react/nativemodule/bridging"])
+
+  if ENV["USE_HERMES"] == nil || ENV["USE_HERMES"] == "1"
+    s.dependency "hermes-engine"
+  else
+    s.dependency "React-jsc"
+  end
+
+
+  s.script_phases = [
+    {
+      :name => '[RN]Check FBReactNativeSpec',
+      :execution_position => :before_compile,
+      :script => <<-EOS
+echo "Checking whether Codegen has run..."
+fbReactNativeSpecPath="$REACT_NATIVE_PATH/React/FBReactNativeSpec"
+
+if [[ ! -d "$fbReactNativeSpecPath" ]]; then
+  echo 'error: Codegen did not run properly in your project. Please reinstall cocoapods with `bundle exec pod install`.'
+  exit 1
+fi
+      EOS
+    }
+  ]
+end