feature(cli): improve prebuild for arbitrary template platforms (#22201)

# Why

This should improve users who have custom platforms for prebuild, like
`tvos`.

# How

- Lifted the limitation

feature(cli): improve prebuild for arbitrary template platforms (#22201)

# Why

This should improve users who have custom platforms for prebuild, like
`tvos`.

# How

- Lifted the limitation on the `expo prebuild --platform` flag
- Check if the template has `./${platform}` folder before copying files
over

# Examples

<details><summary>Platforms existing in the template</summary>

<img width="924" alt="image"
src="https://user-images.githubusercontent.com/1203991/233436089-c19a1e76-5f6d-4121-8570-a8152f8039fb.png">

</details>

<details><summary>Platforms not existing in the template</summary>

<img width="564" alt="image"
src="https://user-images.githubusercontent.com/1203991/233439559-bbe7cc4f-6272-4991-9d2a-fad302486b0a.png">

</details>

# Test Plan

- `$ yarn create expo-app ./test-platforms`
- `$ cd ./test-platforms`
- `$ yarn expo prebuild --platform windows --template
https://github.com/microsoft/react-native-windows-samples/tree/main/samples/AppServiceDemo`

The last step should use the `./windows` folder from the
[AppServiceDemo](https://github.com/microsoft/react-native-windows-samples/tree/main/samples/AppServiceDemo)
as template files inside this project.

If there are any plugins defined for that platform, they should be
picked up automatically.

# Checklist

<!--
Please check the appropriate items below if they apply to your diff.
This is required for changes to Expo modules.
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- [ ] Documentation is up to date to reflect these changes (eg:
https://docs.expo.dev and README.md).
- [ ] Conforms with the [Documentation Writing Style
Guide](https://github.com/expo/expo/blob/main/guides/Expo%20Documentation%20Writing%20Style%20Guide.md)
- [ ] This diff will work correctly for `expo prebuild` & EAS Build (eg:
updated a module plugin).

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