Support @HttpExchange for server-side handling #30913
Description
While @HttpExchange was initially created for client use, the idea was always that an @HttpExchange interface is an HTTP service contract, neutral to client or server.
In addition to simplifying client code, there are also cases where a shared interface between client and server provides an easy way for clients to access server APIs and keep up with changes. This leads to increased coupling that won't be a good fit for a public API but may be exactly the goal for internal APIs. This is commonly used with Spring Cloud and OpenFeign as described in #30733 (comment).
Similar support is also planned for the RSocket interface client in #29240.