Update `SpringBootContextLoader` so that it now implements the
`AotContextLoader` interface. The `ContextLoaderHook` will abandon
at `contextLoaded` if the test class is being AOT processed.
This commit also introduces a new `AotApplicationContextInitializer`
which allows us to plug-in an alternative AOT application context
listener when the `SpringApplication` is running in test mode.
Closes gh-31965