GrpcService.prototype.createFetchHandler(): RpcFetchHandler
Deprecated
Since M70a the kernel dispatches gRPC itself, after the
middleware pipeline, so nothing installs this handler — the pre-pipeline
interceptor was the security defect that change closed. Use
GrpcService.claims together with
GrpcService.handleRequest instead. Retained because
GrpcService is published surface (AI_GUIDELINES §9.2).
The handler that used to be installed into IHttpAdapter.setRpcHandler.
Returns null for any request outside basePath.