Add proper SPIs for the Quarkus integration

Due to the lack of appropriate SPIs, the Hibernate Search extension for Quarkus is forced to rely on dodgy practices:

• It "substitutes" code of methods, which is fine, but it does so in internal methods, whose signature or behavior could change at any time.

• It maintains a list of classes that require reflection (such as the classes serialized through Gson), but at least some of those classes are internal classes whose name or package could change at any time.

• : maybe you can add more here?

We should find a way to define SPIs to avoid such practices.