refactor: Replace System.err.println with log output (#3600)

Auto-cherry-pick to 1.0.x
Fixes #3600

Signed-off-by: Sun Yuhan <sunyuhan1998@users.noreply.github.com>
Co-authored-by: Sun Yuhan <sunyuhan1998@users.noreply.github.com>

Author: sunyuhan1998

document-readers/pdf-reader/src/main/java/org/springframework/ai/reader/pdf/layout/ForkPDFLayoutTextStripper.java

@@ -27,6 +27,8 @@
 import org.apache.pdfbox.text.PDFTextStripper;
 import org.apache.pdfbox.text.TextPosition;
 import org.apache.pdfbox.text.TextPositionComparator;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * This class extends PDFTextStripper to provide custom text extraction and formatting
@@ -38,6 +40,8 @@
  */
 public class ForkPDFLayoutTextStripper extends PDFTextStripper {
 
+	private final static Logger logger = LoggerFactory.getLogger(ForkPDFLayoutTextStripper.class);
+
 	public static final boolean DEBUG = false;
 
 	public static final int OUTPUT_SPACE_CHARACTER_WIDTH_IN_PT = 4;
@@ -80,7 +84,7 @@ protected void writePage() throws IOException {
 				this.sortTextPositionList(textList);
 			}
 			catch (java.lang.IllegalArgumentException e) {
-				System.err.println(e);
+				logger.error("Error sorting text positions", e);
 			}
 			this.iterateThroughTextList(textList.iterator());
 		}