Add new architecture cpp-app template for init-windows

[jonthysell]

Description

This PR adds the starting template for a purely "new architecture" RNW app, based on our current progress in implementing turbo modules and fabric. It also makes some supporting changes such as making sure run-windows still works and adding new non-UWP external property sheets.

Type of Change

• New feature (non-breaking change which adds functionality)

Why

This gives us the ability to start experimenting with fabric apps outside of the specialized versions in our repo.

Closes #11908
Closes #12171

What

Created a new generalized app template based on the e2e-test-app-fabric test app and the first minimal sample RNW fabric app here: https://github.com/chiaramooney/sample-fabric/.

This template can be used to initialize a new RNW app using all new architecture features, on an existing react-native project.

Once checked in, folks should be able to try this out with some variant of:

npx react-native@latest init testlocal --version 0.73.0-nightly-20230811-68c7cfe62
cd testlocal
yarn add react-native-windows@canary
yarn react-native init-windows --template cpp-app --overwrite --logging
yarn react-native run-windows --no-autolink --logging

Metro should start as well as launch the packaged version of your app.

Screenshots

Testing

I created a new project (using my linked local RNW repo) using the following:

npx react-native@latest init testlocal --version 0.73.0-nightly-20230811-68c7cfe62
cd testlocal
yarn add react-native-windows@canary && yarn link react-native-windows
yarn react-native init-windows --template cpp-app --overwrite --logging
yarn react-native run-windows --no-autolink --logging

Changelog

Should this change be included in the release notes: no

Microsoft Reviewers: Open in CodeFlow