PR #32215 added the verified root cert subject to the lower level
`tsi_peer`. This PR is a companion to that and completes the feature by
bubbling the information up to the `TsiCustomVerificationCheckRequest`
which is part of the user facing API for implementing custom
verification callbacks.
* Tooling to remove redundant grpc_core:: namespaces
These references tend to show up in our C++ code after C modules get
converted. Many get caught in review, many get missed.
* use it
* clang-format
Gregory Cooke