INT-4155: Port FTP DSL

JIRA: https://jira.spring.io/browse/INT-4155

- Add streaming support
- Rework tests to use dynamic flow registrations due to the test FTP server is now a test support class.

Javadoc fixes

Checkstyle fix

Polishing - PR Comments

Polishing and Port SFTP

spring-integration-file/src/test/java/org/springframework/integration/file/remote/RemoteFileTestSupport.java

@@ -57,6 +57,10 @@ public abstract class RemoteFileTestSupport {
 		return targetRemoteDirectory;
 	}
 
+	public String getTargetRemoteDirectoryName() {
+		return targetRemoteDirectory.getAbsolutePath() + File.separator;
+	}
+
 	public File getSourceLocalDirectory() {
 		return sourceLocalDirectory;
 	}
@@ -65,6 +69,10 @@ public abstract class RemoteFileTestSupport {
 		return targetLocalDirectory;
 	}
 
+	public String getTargetLocalDirectoryName() {
+		return targetLocalDirectory.getAbsolutePath() + File.separator;
+	}
+
 	/**
 	 * Default implementation creates the following folder structures:
 	 *