Fix carriage return handling in TEXTAREA

Author: sirreal

src/wp-includes/html-api/class-wp-html-tag-processor.php

@@ -3894,7 +3894,10 @@ static function ( $tag_match ) {
 				 * If the intention is to start with a leading newline, ensure that it is preserved
 				 * by adding an additional leading newline.
 				 */
-				if ( 'TEXTAREA' === $this->get_tag() && str_starts_with( $plaintext_content, "\n" ) ) {
+				if (
+					'TEXTAREA' === $this->get_tag() &&
+					1 === strspn( $plaintext_content, "\n\r", 0, 1 )
+				) {
 					$plaintext_content = "\n{$plaintext_content}";
 				}