proc-macros: Support deprecated methods for rpc client (#570)

* proc-macros: Fix documentation typo of `rpc_identifier`

* proc-macros: Support deprecated methods for rpc client (#564)

Calling a deprecated method of the RPC client should warn
the user at compile-time.

Extract the `#[deprecated]` macro as is while parsing the
RpcMethod, and pass through the macro to the RPC client
rendering.

* tests/ui: Check deprecated method for rpc client (#564)

To ensure that the test will fail during compilation,
warnings are denied.

Check that the deprecate macro will generate warnings
just for the methods that are utilized.