Add react-native run-macos command

[tom-un]

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

This change adds a react-native run-macos command similar to run-ios and run-android. It will build the macOS app and then launch it.

The change also modified the macos-generator command to output an updated final message that informs the user to run via npx react-native run-macos.

A minor bug in the macos xcodeproj template is fixed: it was creating an App bundle Id in the form org.reactjs.native.AppName.AppName instead of org.reactjs.AppName.AppName.

The new run-macos command is registered in react-native.config.js for macos platform.

scripts/packager.sh was updated so that when the "Launch Packager" custom build step in React runs, it correctly starts the packager in react-native-macos mode similar to what yarn start:macos does.

This command is patterned after the run-ios command which is implemented at https://github.com/react-native-community/cli/tree/master/packages/platform-ios/src/commands/runIOS.

Focus areas to test

npx react-native init AwesomeApp
cd AwesomeApp
npx react-native-macos-init
npx react-native run-macos

Microsoft Reviewers: Open in CodeFlow

[pull-bot]

	Messages
📖	📋 Missing Changelog - Can you add a Changelog? To do so, add a "## Changelog" section to your PR description. A changelog entry has the following format: [CATEGORY] [TYPE] - Message. CATEGORY may be: General iOS Android JavaScript Internal (for changes that do not need to be called out in the release notes) TYPE may be: Added, for new features. Changed, for changes in existing functionality. Deprecated, for soon-to-be removed features. Removed, for now removed features. Fixed, for any bug fixes. Security, in case of vulnerabilities. MESSAGE may answer "what and why" on a feature level. Use this to briefly tell React Native users about notable changes.
📖	📋 Missing Test Plan - Can you add a Test Plan? To do so, add a "## Test Plan" section to your PR description. A Test Plan lets us know how these changes were tested.
📖	📋 Missing Summary - Can you add a Summary? To do so, add a "## Summary" section to your PR description. This is a good place to explain the motivation for making this change.

Generated by 🚫 dangerJS against 3267418

[analysis-bot]

Code analysis results:

• shellcheck found some issues.

[alloy]

Nice ✨