As per the recent fix to the `always_specify_types` lint (https://github.com/dart-lang/linter/issues/199), literal maps and lists are now expected to be explicitly typed.

Running that lint on the repo identifies quite a few spots to update.  This focuses on `flutter_driver` and `flutter_sprites` (somewhat arbitrarily) but the changes are fairly representative.

Note there are a number of places where I made a quick judgement on how specific to make the types.  Feedback on those is welcome.  (Especially as we move forward with more.)

* Initial set of tests for flutter sprites