pw_rpc: Export wrapper class in Client and Service
pw_rpc: Export wrapper class in Client and Service

Previously, there was no way for templated code to go from a
generated Client or Service template parameter to the generated wrapper
class which contains both the client, server, and other information
about the service (such as the `ServiceId`).

This change re-exports the broader service namespace class inside the
generated `Client` and `Service` classes as
`<ClientType>::ServiceInfo` and `<ServiceType>::ServiceInfo`.

Change-Id: I5ac5d3fd31b217ec454499d547e4fd0ee2a7507b
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/105661
Reviewed-by: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Taylor Cramer <b5aae394837ca396e25263b9eb8b16299f46ca1a@google.com>

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