Based on a handful of https://abseil.io/tips, it's generally advised to
only fully-qualify namespaces when in a `using` statement, or when it's
otherwise required for compilation. In all other cases, the general
recommendation is to not fully-qualify.
This change fixes most `grpc.*` namespace uses. There are potential
challenges in trying to make blanket changes to non-gRPC namespace uses,
such as `::testing`, since there is also a `grpc::testing` namespace.
* De-experimentalize callback API
* Make FromServerContext based on ServerContextBase
* Fix lambda
* Fix headers
* De-experimentalize tests
* clang-format
* Fix consistency checks
* wip
* Fix const-ness of callback client read RPC requests
* Fix golden file
* Give full route_guide callback client example with Hold etc
* Complete example route-guide server
* De-experimentalize test services
* Omit unneeded using
* Remove some uses of non-experimental macro from test
* clang-format examples
* De-experimentalize async stub calls
* Remove experimental namespace use in qps, ubms
* De-experimentalize alarms, generic stubs, and context allocator
* De-experimentalize SetContextAllocator
* clang-format
* Fix conflicts
* Leave obsolete API in place until users can be migrated