saml2-service-provider: OpenSaml4AuthenticationProvider has Java 11 bytecode

[handcraftedbits]

Describe the bug
In contrast to the rest of the classes in spring-security-saml2-service-provider-5.5.0*.jar, OpenSaml4AuthenticationProvider and OpenSaml4AuthenticationRequestFactory contain Java 11 bytecode. These classes are the replacement for OpenSamlAuthenticationProvider and OpenSamlAuthenticationRequestFactory, but users on JVMs < 11 can't use them.

To Reproduce
Attempt to use one of the listed classes on a JVM < 11.

Expected behavior
These classes should be usable on Java 8 JVMs since everything else in the library is.

[eleftherias]

Hi @handcraftedbits, Spring Security's runtime baseline is JDK 8, and it remains that way. However since OpenSAML 4's runtime baseline is JDK 11, an application that uses OpenSAML 4 will need to run with JDK 11.

See gh-9095 for more details and specifically this comment.