feat: run flutter tests with linked aot binaries

[eseidel]

flutter_tester is the underlying binary used by flutter test. Ideally we would run all of the flutter test tests in packages/flutter, just with Shorebird's Dart. The problem is that flutter test currently uses JIT. It runs the .dart files through the frontend server and then sends the .dill files to flutter_tester which compiles and executes them in separate flutter engine instances.

We would probably move to either a one-off flutter_tester to start. Regardless, we would need to change flutter_tester to have an aot-mode, as well as flutter test (or our own simpler harness) to know how to do the aot compile with gen_snapshot.

This could get us a bunch of testing at the flutter level that we don't have today:

• link percentage tests
• before/after linking tests (including performance)

It's at least a couple day project.