Add benchmarks to compare performance metrics between Flutter and native equivalent apps

Add benchmarks for key performance metrics to compare a Flutter app with an equivalent native app.

Create benchmarking app for flutter. It should have minimal assets, ios only, (optional) with endless scrolling. #162025
Create equivalent app for SwiftUI. #162026
Move the app and scripts to flutter/flutter benchmarks
Add new benchmarks for Flutter
Add new benchmarks for SwiftUI
- App Size
- Compile Time
- Time To First Frame
- Scrolling
Hook up the metrics to Skiaperf benchmarks
Make sure all benchmarks are added to Skiaperf benchmarks alerts (the regex just changed so it may need to be added explicitly).

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