Register RateLimitRoute

Summary:
`RateLimitRoute` already existed and worked as an mcrouter route handle; the capability was simply missing from the Carbon-generated `BigCacheRouterInfo` route-handle map.

BigCache therefore could not construct a config that named it: parsing threw `Unknown RouteHandle: RateLimitRoute`, and the uncaught exception in `createRaw()` could crash RevProxy workers.

This diff plugs that registration gap through constrained factory overloads, the `BigCache.idl` opt-in, and regenerated Carbon output. It changes no routing or wire semantics and follows code-before-config ordering, so it is inert on land until a BigCache config activates the route.

`IsRouterInfo<T>` detects at compile time whether `T` exposes `RouteHandleIf`, `RouteHandlePtr`, and `RoutableRequests`.

This change implements concept, which allows the new `RouterInfo` overload, constrained to `IsRouterInfo<T>`, only unwraps `RouterInfo::RouteHandleIf` and delegates to that implementation without duplicating logic.

Reviewed By: lenar-f

Differential Revision: D114367253

fbshipit-source-id: 3a6cf45696a638fc2cce059392418438f20f1dd5

Author: Will Wang

mcrouter/routes/RateLimitRoute.h

@@ -27,6 +27,17 @@ class RouteHandleFactory;
 
 namespace mcrouter {
 
+namespace detail {
+
+template <class T>
+concept RouterInfoLike = requires {
+  typename T::RouteHandleIf;
+  typename T::RouteHandlePtr;
+  typename T::RoutableRequests;
+};
+
+} // namespace detail
+
 /**
  * Requests sent through this route will be rate limited according
  * to settings in the RateLimiter passed to the constructor.
@@ -87,6 +98,7 @@ std::shared_ptr<RouteHandleIf> createRateLimitRoute(
 }
 
 template <class RouteHandleIf>
+  requires(!detail::RouterInfoLike<RouteHandleIf>)
 std::shared_ptr<RouteHandleIf> makeRateLimitRoute(
     RouteHandleFactory<RouteHandleIf>& factory,
     const folly::dynamic& json) {
@@ -107,6 +119,13 @@ std::shared_ptr<RouteHandleIf> makeRateLimitRoute(
       std::move(target), RateLimiter(*jrates), std::move(fallback));
 }
 
+template <detail::RouterInfoLike RouterInfo>
+typename RouterInfo::RouteHandlePtr makeRateLimitRoute(
+    RouteHandleFactory<typename RouterInfo::RouteHandleIf>& factory,
+    const folly::dynamic& json) {
+  return makeRateLimitRoute<typename RouterInfo::RouteHandleIf>(factory, json);
+}
+
 } // namespace mcrouter
 } // namespace memcache
 } // namespace facebook