Previously, SpringApplicationShutdownHook would call close() on any
registered application context even if it wasn't active as it had
already been closed. This could lead to deadlock if the context was
closed and System.exit was called during application context refresh.

This commit updates SpringApplicationShutdownHook so that it only
calls close() on active contexts. This prevents deadlock as it avoids
trying to sychronize on the context's startupShutdownMonitor on
the shutdown hook thread while it's still held on the main thread
which called System.exit and is waiting for all of the shutdown hooks
to complete.

Fixes gh-27049