3657 [url_launcher] Migrate unit tests to NNBD (cla: yes, p: url_launcher)

3658 [device_info] Enable NNBD for unit test (cla: yes, p: device_info)

3659 [android_intent] move unit test to nullsafety (cla: yes, p: android_intent, waiting for tree to go green)

3660 [share] Migrate unit tests to null-safety. (cla: yes, p: share, waiting for tree to go green)

3661 Remove unused plugin (integration_test_macos) (cla: yes, p: integration_test, platform-macos, waiting for tree to go green)