Improve fixture package scripts and add CI

[mattfrances]

Description

Improves the fixture app's package scripts and adds CI.

The package scripts added are:

• up: Prepares restyle and also the fixture app through fixture up
• fixture up: Prepares the fixture app by running yarn and installing pods for iOS
• start: Runs metro
• run-ios: Runs the iOS fixture app
• run-android: Runs the Android fixture app

For CI, this PR adds pipelines to build the fixture's TypeScript code and build the Android app. We decided to not build the iOS app as it would take ~30mins (see time in flashlist for reference). Since updates to the app will generally not contain native code, this check is not entirely necessary and we will add it in the future if it does become needed.

Reviewers’ hat-rack :tophat:

1. CI ✅
2. Run the package scripts above in the root folder using yarn <command> and confirm that they all work properly

Screenshots or videos (if needed)

Checklist

• [ ] I have added a changelog entry following the Keep a Changelog guidelines.

[mattfrances]

The only thing, can we leave a comment or a decision log about skipping iOS build on CI? I could see future maintainers being confused by it.

Great point, added it in!