SERVER-131199 added an opCtx->getClient()->isInDirectClient() call to IncrementalFeatureRolloutContext::get() in feature_flag.cpp, which is part of the server_base library. The calls are inline so normal builds are unaffected, but UBSan's vptr sanitizer emits references to typeinfo for mongo::Client and typeinfo for mongo::OperationContext, which are defined only in service_context. Binaries that link server_base without service_context (e.g. ksdecode_with_debug) fail to link on the UBSan all-feature-flags variants, breaking archive_dist_test on master since 2a98177057 (BF-44767).

Fix: move the opCtx-coupled statics (get/tryGet/isInstalled/set/installForRequestWithoutIfrFlags and the opCtx decoration) into a new ifr_context_decoration.cpp in the service_context target, mirroring the existing version_context_decoration.cpp split. No behavior change.