Provide access to AbstractRoutingDataSource's resolved target DataSources #25544
Description
We've had a few Spring Boot issues related to metrics and health where it would be useful to have access to an AbstractRoutingDataSource's resolved targets (spring-projects/spring-boot#22719, spring-projects/spring-boot#22222). Having access to the resolved targets would allow us to automatically provide metrics and health information for the target DataSources without them having to be exposed as beans or without the user having to write so much code to register them for metrics and health manually.