At the request of the Spring Boot team, ApplicationContextFailureProcessor
implementations are now loaded via the spring.factories mechanism
instead of supporting a single processor registered via subclasses of
AbstractTestContextBootstrapper.
This makes the retrieval and handling of processors internal to
DefaultCacheAwareContextLoaderDelegate, while simultaneously supporting
multiple processors that can be registered by anyone (i.e., not
limited to projects that implement custom TestContextBootstrappers).
See gh-28826
Closes gh-29387
a13cb01b99