This fills out the following matrix:
App: `flutter create` default app, Complex Layout, and Gallery.
Platforms: Linux/Android, Mac/iOS, Windows/Android
Build modes: full release, aot blobs, debug
Dart: normal, 2.0 preview
It also renames all the tests that used "build" to mean compilation
build to use "compile" instead, so that it's much clearer on the
dashboard.
Also, mark some flaky tests that are no longer flaky as not flaky.
Also, remove uses of call() since that's probably going to go away at
some point.
