Support Windows path in ContentDisposition::parse

This commit makes sure that ContentDisposition::parse supports Windows
path with a backslash.

Closes gh-30111

spring-web/src/main/java/org/springframework/http/ContentDisposition.java

@@ -624,7 +624,11 @@ public final class ContentDisposition {
 			char c = filename.charAt(i);
 			if (filename.charAt(i) == '\\' && i + 1 < length) {
 				i++;
-				sb.append(filename.charAt(i));
+				char next = filename.charAt(i);
+				if (next != '"' && next != '\\') {
+					sb.append(c);
+				}
+				sb.append(next);
 			}
 			else {
 				sb.append(c);