feat: add react-native-macos support (#513)

* Move example -> example-prev

* Init React Native Test App

yarn init-test-app --version 0.73.0
(and manually bump react-native-* versions afterwards)

* Merge example-prev into example

* Add osx to podspec

* Fix metro config to resolve react-native-safe-area-context

* Install pods

* Write macOS equivalents for all iOS code

* Raise macOS deployment target to 10.15

* Delete example-prev

* Trying and failing to get macOS app to build

* Apply Tommy Nguyen's suggestions to fix pod installation

Co-authored-by: Tommy Nguyen <4123478+tido64@users.noreply.github.com>

* Stop using compat components for macOS

* Restore example to its original state

* Add example-macos

* Reduce macOS deployment target to 10.15

* Make example-macos use RNTesterApp instead of bespoke app

* Remove example-macos

* Pin react-native and react-native-macos to v0.74

* Init react-native-macos@0.74 project

I temporarily renamed the "name" field in package.json to "RNSACExample", then ran `npx react-native-macos-init` to generate a project by that name.

* Fix bundleURL

microsoft/react-native-macos#2164 (comment)

* Fix Metro config

* Run yarn format:write

---------

Co-authored-by: Tommy Nguyen <4123478+tido64@users.noreply.github.com>

example/macos/.gitignore

@@ -0,0 +1,2 @@
+# CocoaPods
+Pods/

example/macos/.xcode.env

@@ -0,0 +1 @@
+export NODE_BINARY=$(command -v node)

example/macos/Podfile

@@ -0,0 +1,24 @@
+require_relative '../node_modules/react-native-macos/scripts/react_native_pods'
+require_relative '../node_modules/@react-native-community/cli-platform-ios/native_modules'
+
+prepare_react_native_project!
+
+target 'RNSACExample-macOS' do
+  platform :macos, '10.15'
+  use_native_modules!
+
+  # Flags change depending on the env values.
+  flags = get_default_flags()
+
+  use_react_native!(
+    :path => '../node_modules/react-native-macos',
+    :hermes_enabled => false,
+    :fabric_enabled => ENV['RCT_NEW_ARCH_ENABLED'] == '1',
+    # An absolute path to your application root.
+    :app_path => "#{Pod::Config.instance.installation_root}/.."
+  )
+
+  post_install do |installer|
+    react_native_post_install(installer)
+  end
+end