Add newline at the beginning of textarea JSP tags

This commit adds a newline char at the beginning of textarea tags
values. As per the HTML 4.01 spec (and browsers behavior), a line break
following a start tag is ignored.

This can lead to Spring's textarea tag to ignore a line break char at
the beginning of a tag value.

See https://www.w3.org/TR/html401/appendix/notes.html#notes-line-breaks

Issue: SPR-13503
Cherry picked from 44c3212

Author: bclozel

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/TextareaTag.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -98,7 +98,7 @@ protected int writeTagContent(TagWriter tagWriter) throws JspException {
 		writeOptionalAttribute(tagWriter, COLS_ATTRIBUTE, getCols());
 		writeOptionalAttribute(tagWriter, ONSELECT_ATTRIBUTE, getOnselect());
 		String value = getDisplayString(getBoundValue(), getPropertyEditor());
-		tagWriter.appendValue(processFieldValue(getName(), value, "textarea"));
+		tagWriter.appendValue("\r\n" + processFieldValue(getName(), value, "textarea"));
 		tagWriter.endTag();
 		return SKIP_BODY;
 	}

spring-webmvc/src/test/java/org/springframework/web/servlet/tags/form/TextareaTagTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -121,6 +121,16 @@ public void customBind() throws Exception {
 		assertBlockTagContains(output, "12.34f");
 	}
 
+	@Test
+	public void firstNewLine() throws Exception {
+		this.tag.setPath("name");
+		this.tag.setReadonly(true);
+
+		assertEquals(Tag.SKIP_BODY, this.tag.doStartTag());
+		String output = getOutput();
+		assertBlockTagContains(output, "\r\nRob");
+	}
+
 	@Override
 	protected TestBean createTestBean() {
 		// set up test data