Access connection factory from DatabaseClient

This commit provides an accessor for the underlying ConnectionFactory
that a DatabaseClient uses.

Closes gh-25521

spring-r2dbc/src/main/java/org/springframework/r2dbc/core/DatabaseClient.java

@@ -55,6 +55,12 @@ import org.springframework.util.Assert;
  */
 public interface DatabaseClient extends ConnectionAccessor {
 
+	/**
+	 * Return the {@link ConnectionFactory} that this client uses.
+	 * @return the connection factory
+	 */
+	ConnectionFactory getConnectionFactory();
+
 	/**
 	 * Specify a static {@code sql} statement to run. Contract for specifying a
 	 * SQL call along with options leading to the execution. The SQL string can

spring-r2dbc/src/main/java/org/springframework/r2dbc/core/DefaultDatabaseClient.java

@@ -85,6 +85,11 @@ class DefaultDatabaseClient implements DatabaseClient {
 	}
 
 
+	@Override
+	public ConnectionFactory getConnectionFactory() {
+		return this.connectionFactory;
+	}
+
 	@Override
 	public GenericExecuteSpec sql(String sql) {
 		Assert.hasText(sql, "SQL must not be null or empty");