Not updating the example WORKSPACE because it doesn't have any
Bazel-enabled build that depends on xds and so doesn't need the
additional repository dependencies.
Fixes#9162
* api: add support for SocketAddress types in ManagedChannelProvider
also add support for SocketAddress types in NameResolverProvider
Use scheme in target URI to select a NameRseolverProvider and get
that provider's supported SocketAddress types.
implement selection in ManagedChannelRegistry of appropriate
ManagedChannelProvider based on NameResolver's SocketAddress types
GoogleCloudToProdNameResolver has a hard dependency on alts whereas xds
only has a weak dependency on alts that can be solved by a
ChannelCredentialsRegistry. So split out the code to a separate
artifact.
Alexander Polcyn