Prior to this commit, SpringFactoriesLoader discovered all registered
factory implementations for a given factory type even if duplicates
were registered within a single META-INF/spring.factories file or in
multiple such files in the classpath.
This commit updates the internals of SpringFactoriesLoader so that
duplicate registrations are ignored, thereby aligning with the
well-known semantics for java.util.ServiceLoader in this regard.
Closes gh-24985
