Sorbet / Tapioca DSL support

I've opened https://github.com/Shopify/tapioca/issues/2235 but the core issue is that we lose the type information from the GRPC DSL that tapioca provides when the twirp layer is added, so unfortunately calls to `twirp-ruby` in ruby apps with Sorbet do not get the benefit of type information, as the twirp layer adds a lay of indirection which leads to the interfaces all being untyped.

It would be amazing if it were possible to provide this somehow.

Start with the linked Shopify/tapioca#2235 issue and trace how the Twirp layer currently exposes service interfaces to Ruby callers. No file or test is named; done means Sorbet/Tapioca retains the gRPC DSL type information through the Twirp layer, with the behavior covered by an appropriate regression test.

Written by the indexing model from the issue text.