Fix breaking change for PersistentFileListFilter

The `AbstractPersistentAcceptOnceFileListFilter`
extends now an `AbstractDirectoryAwareFileListFilter`
and makes all the implementors to implement its `isDirectory()` method.
This is a breaking change in the point release which makes implementations
outside of the core project not compilable

The regression after: #3488
Related fix in the Spring Cloud GCP: spring-attic/spring-cloud-gcp#2654

* Implement an `isDirectory()` in the `AbstractPersistentAcceptOnceFileListFilter`
to let other implementations do not worry during upgrade

**Cherry-pick to `5.4.x` & `5.3.x`**

Author: artembilan

spring-integration-file/src/main/java/org/springframework/integration/file/filters/AbstractPersistentAcceptOnceFileListFilter.java

@@ -180,6 +180,11 @@ protected void flushIfNeeded() {
 		}
 	}
 
+	@Override
+	protected boolean isDirectory(F file) {
+		return false;
+	}
+
 	protected abstract long modified(F file);
 
 	protected abstract String fileName(F file);

spring-integration-file/src/test/java/org/springframework/integration/file/filters/PersistentAcceptOnceFileListFilterTests.java

@@ -111,11 +111,6 @@ protected String fileName(String file) {
 						return file;
 					}
 
-					@Override
-					protected boolean isDirectory(String file) {
-						return false;
-					}
-
 				};
 		doTestRollback(filter);
 	}

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

@@ -345,19 +345,19 @@ public Session<String> getSession() {
 			}
 			try {
 				Session<String> session = mock(Session.class);
-				willReturn(new String[] { "/foo/foo", "/foo/bar" }).given(session).list("/foo");
+				willReturn(new String[]{ "/foo/foo", "/foo/bar" }).given(session).list("/foo");
 				ByteArrayInputStream foo = new ByteArrayInputStream("foo\nbar".getBytes());
 				ByteArrayInputStream bar = new ByteArrayInputStream("baz\nqux".getBytes());
 				willReturn(foo).given(session).readRaw("/foo/foo");
 				willReturn(bar).given(session).readRaw("/foo/bar");
 
-				willReturn(new String[] { "/bar/foo", "/bar/bar" }).given(session).list("/bar");
+				willReturn(new String[]{ "/bar/foo", "/bar/bar" }).given(session).list("/bar");
 				ByteArrayInputStream foo2 = new ByteArrayInputStream("foo\r\nbar".getBytes());
 				ByteArrayInputStream bar2 = new ByteArrayInputStream("baz\r\nqux".getBytes());
 				willReturn(foo2).given(session).readRaw("/bar/foo");
 				willReturn(bar2).given(session).readRaw("/bar/bar");
 
-				willReturn(new String[] { "/bad/file1", "/bad/file2" }).given(session).list("/bad");
+				willReturn(new String[]{ "/bad/file1", "/bad/file2" }).given(session).list("/bad");
 				willThrow(new IOException("No file")).given(session).readRaw("/bad/file1");
 				willThrow(new IOException("No file")).given(session).readRaw("/bad/file2");
 
@@ -390,11 +390,6 @@ protected String fileName(String file) {
 			return file;
 		}
 
-		@Override
-		protected boolean isDirectory(String file) {
-			return false;
-		}
-
 	}
 
 }