Delegation support for JDBC 4.3 ConnectionBuilder and ShardingKeyBuilder

[jhoeller]

The JDBC 4.3 methods createConnectionBuilder() and createShardingKeyBuilder() (available as of JDK 9) have default implementations which just throw a not-supported exception. For Spring's DelegatingDataSource and AbstractRoutingDataSource, we can introduce delegation support for those methods, invoking the corresponding methods on the target DataSource. This makes it available on all of Spring's common DataSource adapters and proxies - usually without special decoration but at least allowing the same degree of access as on the target DataSource itself.

This goes along with #31506.