Introduce new syntax in IDL compiler to allow generating
registration/sending code for RPC verbs:
```
verb [[attr1, attr2...] my_verb (args...) -> return_type;
```
`my_verb` RPC verb declaration corresponds to the
`netw::messaging_verb::MY_VERB` enumeration value to identify the
new RPC verb.
For a given `idl_module.idl.hh` file, a registrator class named
`idl_module_rpc_verbs` will be created if there are any RPC verbs
registered within the IDL module file.
These are the methods being created for each RPC verb:
```
static void register_my_verb(netw::messaging_service* ms, std::function<return_type(args...)>&&);
static future<> unregister_my_verb(netw::messaging_service* ms);
static future<> send_my_verb(netw::messaging_service* ms, netw::msg_addr id, args...);
```
Each method accepts a pointer to an instance of `messaging_service`
object, which contains the underlying seastar RPC protocol
implementation, that is used to register verbs and pass messages.
There is also a method to unregister all verbs at once:
```
static future<> unregister(netw::messaging_service* ms);
```
The following attributes are supported when declaring an RPC verb
in the IDL:
* `[[with_client_info]]` - the handler will contain a const reference to
an `rpc::client_info` as the first argument.
* `[[with_timeout]]` - an additional `time_point` parameter is supplied
to the handler function and `send*` method uses `send_message_*_timeout`
variant of internal function to actually send the message.
* `[[one_way]]` - the handler function is annotated by
`future<rpc::no_wait_type>` return type to designate that a client
doesn't need to wait for an answer.
The `-> return_type` clause is optional for two-way messages. If omitted,
the return type is set to be `future<>`.
For one-way verbs, the use of return clause is prohibited and the
signature of `send*` function always returns `future<>`.
No existing code is affected.
Ref: #1456Closes#9359
* github.com:scylladb/scylla:
idl: support generating boilerplate code for RPC verbs
idl: allow specifying multiple attributes in the grammar
message: messaging_service: extract RPC protocol details and helpers into a separate header
0ea79559a6