* Use Xcode build configurations to drive Flutter build mode
* Proper check wrt local_engine, print error if profile mode misisng
* Remove unused code, update tests, fix template problem, update warning
* fix up warning
* add explanatory dev comment
* fix whitespace
* missing words, change lambda arrow to function body
* error indentation
* Test early exits for xcode_backend.sh
* only on macOS, use right test
* Update error messages
* case insensitive compare for build config
* Update gallery podfile
* update projects to add profile configuration
* make compatible with flavors
* add missing plist files
Generated.xcconfig is only required at build time for iOS apps. In the
flutter create project template and example apps, Generated.xcconfig was
previously marked as a resource to be bundled into the built app.
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.
