Adds a buildbucket package. (#2324)

* Temporarily add logging of results messages.

This will give us visibility of the message format required to report
results from builders from dart-internal.

* Adds a buildbucket package.

Dart & Flutter use buildbucket extensively and we have been replicating
the parsing logic in multiple places instead of using the protos
directly. This package provides compiled protos for the interaction with
buildbucket V2.

Bug: https://github.com/flutter/flutter/issues/115490

* Revert changes to handler.

* Revert changes handler.

* Revert handler.

* Fix licenses and address comments.

* Ignore generated proto files during analysis.

* Remove ws from bash script.

* Format generated files.
diff --git a/tests.yaml b/tests.yaml
index d9e77d7..e2723a4 100644
--- a/tests.yaml
+++ b/tests.yaml
@@ -37,3 +37,6 @@
 
   - task: device_doctor
     script: test_utilities/bin/dart_test_runner.sh
+
+  - task: packages/buildbucket-dart
+    script: test_utilities/bin/dart_test_runner.sh