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
  • App Size for Flutter #162028
  • Compile Time for Flutter #162029
  • Time to first frame #162030
  • Scrolling #162031
• 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).

Design Doc/Inspo: flutter.dev/go/ui-imitation-games