This is to use `grpc_core::RefCount` to improve performnace.
This commit also replaces explicit C vtables, with C++ vtable
with its own compile time assertions and performance benefits.
It also makes use of `RefCountedPtr` wherever possible.
As opposed to a flat directory, we now have the following structure:
- security
-context
- credentials
- composite
- fake
- google_default
- iam
- jwt
- oauth2
- plugin
- ssl
- transport
- util
We have not refactored the test code yet but this PR is already large
enough...
- Right now it is a global function: would be better to have this per
(secure) port.
- Changed the interface of the auth_context slightly to make it more
friendly.
- Positive tests pass. Still need some work on error case (have a
negative case as well).
- Fixing cpp auth context tests so that they use the shiny new C API.