[jnigen] Stress tests and a few runtime fixes (https://github.com/dart-lang/jnigen/issues/264)

* Generate and compare both types of bindings
* Add load tests
* Add test cases against exception throwing
* add to_global_ref_result function to dartjni.h
* Fix field getter double call in certain cases
108 files changed
tree: 09532e3458e5c5011f52e9cacb233bbb76234651
  1. .github/
  2. pkgs/