Towards https://github.com/flutter/flutter/issues/161333.
This adds the initial `.ci.yaml` configuration (marked `bringup: true`),
without changing the existing shard to avoid the problems we ran into
last time when I renamed the shard atomically, as well as piping for
providing context in which the test will run (Vulkan or OpenGLES), which
can't be introspected in the _running_ app.
In a follow-up PR I'll:
- Edit `AndroidManifest.xml` before the suite, setting `ImpellerBackend`
appropriately
- Move the bringup nodes to presubmit
- Delete the existing (legacy) node
30f4fecfeb