An alias to a repo revision.
A CloudRepoSourceContext denotes a particular revision in a Google Cloud
Source Repo.
A SourceContext referring to a Gerrit project.
A GitSourceContext denotes a particular revision in a third party Git
repository (e.g., GitHub).
Selects a repo using a Google Cloud Platform project ID (e.g.,
winged-cargo-31) and a repo name within that project.
A unique identifier for a Cloud Repo.
A SourceContext is a reference to a tree of files. A SourceContext together
with a path point to a unique revision of a single file or directory.