Calculator C++/WinRT Sample - React Native for Windows

See ../README.md for details of this sample.

See ../csharp/ for a C# version of this sample.

It currently targets React Native Windows 0.78.

To upgrade this sample to the latest version of RNW:

Open a command prompt and navigate to the samples/Calculator folder:
```
cd ..
```
Delete this folder:
```
rd /s /q cppwinrt
```
Create a new React Native app and change version to version you want to upgrade to (replace 'version' with desired version - for latest version, use 'latest'):
```
npx @react-native-community/cli@latest init Calculator --template @react-native-community/template@latest --skip-git-init
```
Add a lockfile to the calculator directory:
```
cd Calculator
yarn install
```

Add Windows support:

yarn add react-native-windows@latest
npx @react-native-community/cli@latest init-windows --template old/uwp-cpp-app --overwrite

Restore these original app files:

cd cppwinrt
git restore README.md
git restore App.tsx

Verify the new app builds and runs:

npx @react-native-community/cli@latest run-windows

Look at the Package.appxmanifast and change the publisher name to "CN=React Native Windows Sample". Revert all changes made to GUID values in the project and solution files.
Update this readme with the new major version at the top.

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