This commit reverts changes to AbstractCacheManager since iterating
over the caches in a for-loop and a stream is duplicated effort.
This commit reverts changes to DefaultRenderingResponseBuilder,
RouterFunctions, and OriginHandshakeInterceptor since order matters for
those use cases: they were originally based on the semantics of
LinkedHashSet or LinkedHashMap; whereas, Set.copyOf() and Map.copyOf()
do not provide any guarantees regarding ordering.
This commit also applies analogous changes to "sibling" implementations
across Servlet mocks as well as Web MVC and WebFlux.
See gh-29321