
This consolidates all of the non-template .gitignore rules into the top level .gitignore, to ignore common things more broadly, with less maintenance needed for the .gitignore files. Does not touch the templates, so that they still produce needed .gitignores as part of flutter create.
microbenchmarks
To run these benchmarks on a device, first run `flutter logs' in one window to see the device logs, then, in a different window, run any of these:
flutter run --release lib/gestures/velocity_tracker_data.dart
flutter run --release lib/stocks/animation_bench.dart
flutter run --release lib/stocks/build_bench.dart
flutter run --release lib/stocks/layout_bench.dart
The results should be in the device logs.