Specifically:
- use `OrphanablePtr<>` for `grpc_endpoint`
- use `absl::AnyInvocable<>` instead of `grpc_closure`
- use `EventEngine::Run()` instead of `ExecCtx::Run()`
- use `SliceBuffer` instead of `grpc_slice_buffer`
- use `absl::Status` instead of `grpc_error_handle`
- use `absl::string_view` instead of `const char*` for handshaker names
Also pass acceptor via `HandshakerArgs` instead of as a separate parameter.
Also changed chttp2 and httpcli to use `OrphanablePtr<>` for the endpoint.
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DO NOT SUBMIT. This PR is for testing purposes only. [cl/602805376](http://cl/602805376)
PiperOrigin-RevId: 602805376
3642c9d499