[Monorepo] Add CommonApp (#3496)

## Description

This PR adds `CommonApp` that holds shared source code for our examples.

## Test plan

Run `ExpoExample` and `MacOSExample`

Author: m-bert

apps/CommonApp/.eslintrc.js

@@ -0,0 +1,4 @@
+module.exports = {
+  root: true,
+  extends: '@react-native',
+};

apps/CommonApp/.gitignore

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+# OSX
+#
+.DS_Store
+
+# Xcode
+#
+build/
+*.pbxuser
+!default.pbxuser
+*.mode1v3
+!default.mode1v3
+*.mode2v3
+!default.mode2v3
+*.perspectivev3
+!default.perspectivev3
+xcuserdata
+*.xccheckout
+*.moved-aside
+DerivedData
+*.hmap
+*.ipa
+*.xcuserstate
+**/.xcode.env.local
+
+# Android/IntelliJ
+#
+build/
+.idea
+.gradle
+local.properties
+*.iml
+*.hprof
+.cxx/
+*.keystore
+!debug.keystore
+.kotlin/
+
+# node.js
+#
+node_modules/
+npm-debug.log
+yarn-error.log
+
+# fastlane
+#
+# It is recommended to not store the screenshots in the git repo. Instead, use fastlane to re-generate the
+# screenshots whenever they are needed.
+# For more information about the recommended setup visit:
+# https://docs.fastlane.tools/best-practices/source-control/
+
+**/fastlane/report.xml
+**/fastlane/Preview.html
+**/fastlane/screenshots
+**/fastlane/test_output
+
+# Bundle artifact
+*.jsbundle
+
+# Ruby / CocoaPods
+**/Pods/
+/vendor/bundle/
+
+# Temporary files created by Metro to check the health of the file watcher
+.metro-health-check*
+
+# testing
+/coverage
+
+# Yarn
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/sdks
+!.yarn/versions

apps/CommonApp/.prettierrc.js

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+module.exports = {
+  arrowParens: 'avoid',
+  bracketSameLine: true,
+  bracketSpacing: false,
+  singleQuote: true,
+  trailingComma: 'all',
+};