Scripts provided in the `ng-dev` command might use local `git`
commands. For such scripts, we keep track of the branch that
has been checked out before the command has been invoked.
We do this so that we can later (upon command completion)
restore back to the original branch. We do not want to
leave the Git repository in a dirty state.
It looks like this logic currently only deals with branches
but does not work properly when a command is invoked from
a detached head. We can make it work by just checking out
the previous revision (if no branch is checked out).
PR Close#37737
GitClient now uses GithubClient for github API interactions. GithubClient is
a class which extends Octokit and provides a member which allows for GraphQL
requests against the Github GraphQL api, as well as providing convenience methods
for common/repeated Github API requests.
PR Close#37593
