* Fixing RouteGuide's C++ Reactor example.
The current method involves locking and unlocking a mutex from different
threads, which isn't allowed. Changing the strategy a bit to address
this.
* Automated change: Fix sanity tests
* Switching to absl::Mutex to annotate usage properly.
* Actually, let's not cover the examples with sanity checks.
* 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
Ilya Lukin
Nicolas Noble
Craig Tiller
Vijay Pai