feat(cli, metro-config): environment variable support (#21983)

# Why

- It's nice to be able to use uncommitted values in your app, based on
the environment. This feels very familiar to web devel

feat(cli, metro-config): environment variable support (#21983)

# Why

- It's nice to be able to use uncommitted values in your app, based on
the environment. This feels very familiar to web developers.
- Values that are prefixed with `EXPO_PUBLIC_` will be inlined in the
bundle when bundling normally (e.g. not for Node.js).
- `.env` files are loaded into memory and applied to the process during
a run. This also means that they're available in `app.config.js`.
- During development-only, environment variables are exposed on the
`process.env` object (non-enumerable) to ensure they're available
between fast refresh updates.
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# How

- Create new package `@expo/env` which is used to hydrate env variables
in a unified way. I plan to open another PR in `eas-cli` which uses this
package to fill in environment variables before uploading. NOTE:
environment variables that are defined in eas.json are not available in
Expo CLI when building locally, but are available in the cloud since
they'll be on the process, this means they effectively emulate
`.env.production`.
- Update templates to gitignore local env files.
- Add basic documentation to the versioned metro guide (more to come).


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# Test Plan

- [ ] E2E rendering test
- [ ] E2E Node.js rendering test
- [x] Unit tests for serializer
- [x] Tests for env package

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# Checklist

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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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feat(cli): auto setup typescript during start (#21475)

# Why

- Some users are confused about how to use the fully automated
TypeScript setup. It currently runs when you run `npx expo start` in a

feat(cli): auto setup typescript during start (#21475)

# Why

- Some users are confused about how to use the fully automated
TypeScript setup. It currently runs when you run `npx expo start` in a
project with `tsconfig.json` or any TypeScript file in the project.
- This change will run the TypeScript check continuously until
TypeScript is setup. This only applies to projects using Metro, and
currently is only run in `npx expo start`, and the run commands (when
the server is started in the current window, e.g. not headless mode).

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# How

- Fork the `runServer` function from Metro into the CLI so we can access
the Metro bundler instance directly.
- Use Metro's native file watching to observe new TypeScript files being
added to the project (within the observable files). This is fast and
ensures we don't accidentally block a thread that otherwise could've
been used for bundling.
- The TypeScript continuous check only runs once, if you remove
TypeScript and add it back in the same process, then nothing happens.
This is a performance optimization.
- If TypeScript is enabled while the process is running, the user will
not be prompted to install, the packages will just install in the
project. Failures will be displayed in the running process, and no more
attempts will be made.
- If TypeScript is detected on start then the existing system will be
used and the continuous check will be skipped, this means projects
already using TypeScript won't have any technical performance hit.


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# Test Plan

- In a project without TypeScript:
- `npx expo`
- `touch tsconfig.json` or `mv index.js index.tsx` or `touch foo.tsx`
- TypeScript is automatically installed for the project.
- `EXPO_NO_TYPESCRIPT_SETUP` voids this behavior
- Added unit tests.

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reproduce your test, especially if this PR does not include automated
tests! If possible, please also provide terminal output and/or
screenshots demonstrating your test/reproduction.
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# 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).

---------

Co-authored-by: Expo Bot <[email protected]>
Co-authored-by: Cedric van Putten <[email protected]>

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