Support running tests outside of the test folder with fast "Run All Tests"

When using the fast path for "Run All Tests", only tests inside the `test` folder are run. If you also have `integration_test` etc., they are not run.

This is consistent with running `dart test` in the project, however when there are tests visible _in the test runner_, it feels more odd. We can perhaps use `dart test test integration_test (etc.)` or `dart test .`.