Add patrol tests (#420)

This PR add testing 2 packages that are part of the [Patrol](https://patrol.leancode.co/) testing tool:
- [patrol_cli](https://github.com/leancodepl/patrol/tree/master/packages/patrol_cli)
- ~~[patrol](https://github.com/leancodepl/patrol/tree/master/packages/patrol)~~
- [patrol_finders](https://github.com/leancodepl/patrol/tree/master/packages/patrol_finders)

They relies on multiple dependencies pinned by the Flutter SDK, most heavily on the `flutter_test` API.

Author: piotruela

registry/patrol.test

@@ -0,0 +1,13 @@
+[email protected]
+[email protected]
+[email protected]
+[email protected]
+
+fetch=git clone https://github.com/leancodepl/patrol.git tests
+fetch=git -C tests checkout 8431a501f7de8bec49d4937bd4018266e7ba5ab7
+
+update=packages/patrol_cli
+update=packages/patrol_finders
+
+test.posix=scripts/flutter_test_repo_test.sh
+test.windows=scripts\flutter_test_repo_test.bat