Create RCTAppDelegate to simplify New Architecture Setup (#34384)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/34384

This Diff aims to create a RCTAppDelegate library to offer a subclass which automates some operations required to set up the new architecture.

## Changelog
[iOS][Added] - Added the RCTAppDelegate library

Reviewed By: cortinico

Differential Revision: D38580424

fbshipit-source-id: 38f6c4b8ff2790a2ce9e23d385b36307701cffb7

Libraries/AppDelegate/React-RCTAppDelegate.podspec

@@ -0,0 +1,57 @@
+# 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+  # This is an unpublished version, use the latest commit hash of the react-native repo, which we’re presumably in.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
+
+folly_flags = '-DFOLLY_NO_CONFIG -DFOLLY_MOBILE=1 -DFOLLY_USE_LIBCPP=1'
+folly_compiler_flags = folly_flags + ' ' + '-Wno-comma -Wno-shorten-64-to-32'
+
+new_arch_enabled_flag="RCT_NEW_ARCH_ENABLED"
+is_new_arch_enabled = ENV[new_arch_enabled_flag] == "1"
+other_cflags = "$(inherited) -DRN_FABRIC_ENABLED " + folly_flags + (is_new_arch_enabled ? " -D"+"RCT_NEW_ARCH_ENABLED" : "")
+
+Pod::Spec.new do |s|
+  s.name            = "React-RCTAppDelegate"
+  s.version                = version
+  s.summary                = "An utility library to simplify common operations for the New Architecture"
+  s.homepage               = "https://reactnative.dev/"
+  s.documentation_url      = "https://reactnative.dev/docs/actionsheetios"
+  s.license                = package["license"]
+  s.author                 = "Facebook, Inc. and its affiliates"
+  s.platforms              = { :ios => "12.4" }
+  s.source                 = source
+  s.source_files            = "**/*.{c,h,m,mm,S,cpp}"
+
+  # This guard prevent to install the dependencies when we run `pod install` in the old architecture.
+  s.compiler_flags = other_cflags
+  s.pod_target_xcconfig    = {
+    "HEADER_SEARCH_PATHS" => "\"$(PODS_TARGET_SRCROOT)/ReactCommon\" \"$(PODS_ROOT)/Headers/Private/React-Core\" \"$(PODS_ROOT)/boost\" \"$(PODS_ROOT)/DoubleConversion\" \"$(PODS_ROOT)/RCT-Folly\" \"${PODS_ROOT}/Headers/Public/React-hermes\" \"${PODS_ROOT}/Headers/Public/hermes-engine\" \"${PODS_ROOT}/Headers/Public/FlipperKit\" \"$(PODS_ROOT)/Headers/Public/ReactCommon\" \"$(PODS_ROOT)/Headers/Public/React-RCTFabric\"",
+    "OTHER_CPLUSPLUSFLAGS" => other_cflags,
+    "CLANG_CXX_LANGUAGE_STANDARD" => "c++17"
+  }
+  s.user_target_xcconfig   = { "HEADER_SEARCH_PATHS" => "\"$(PODS_ROOT)/Headers/Private/React-Core\""}
+
+  s.dependency "React-Core"
+  s.dependency "RCT-Folly"
+  s.dependency "RCTRequired"
+  s.dependency "RCTTypeSafety"
+  s.dependency "ReactCommon/turbomodule/core"
+
+  if is_new_arch_enabled
+    s.dependency "React-RCTFabric"
+    s.dependency "React-graphics"
+  end
+end