Fix multipart async servlet request temporary files deletion

This change tracks the multipart nature of the async request
within the `DispatcherServlet`, in the `WebAsyncManager`.

This allows for the second ASYNC dispatch to recognize the
multipart aspect and clean up the associated resources.

Closes gh-33161

Author: simonbasle

Diff for: spring-web/src/main/java/org/springframework/web/context/request/async/WebAsyncManager.java

@@ -79,6 +79,8 @@ public final class WebAsyncManager {
 
 	private AsyncTaskExecutor taskExecutor = DEFAULT_TASK_EXECUTOR;
 
+	private boolean isMultipartRequestParsed;
+
 	@Nullable
 	private volatile Object concurrentResult = RESULT_NONE;
 
@@ -242,6 +244,24 @@ public void registerDeferredResultInterceptors(DeferredResultProcessingIntercept
 		}
 	}
 
+	/**
+	 * Mark the {@link WebAsyncManager} as wrapping a
+	 * multipart async request.
+	 * @since 6.1.12
+	 */
+	public void setMultipartRequestParsed(boolean isMultipart) {
+		this.isMultipartRequestParsed = isMultipart;
+	}
+
+	/**
+	 * Return {@code true} if this {@link WebAsyncManager} was previously marked
+	 * as wrapping a multipart async request, {@code false} otherwise.
+	 * @since 6.1.12
+	 */
+	public boolean isMultipartRequestParsed() {
+		return this.isMultipartRequestParsed;
+	}
+
 	/**
 	 * Clear {@linkplain #getConcurrentResult() concurrentResult} and
 	 * {@linkplain #getConcurrentResultContext() concurrentResultContext}.

Diff for: spring-webmvc/src/main/java/org/springframework/web/servlet/DispatcherServlet.java

@@ -1118,10 +1118,11 @@ protected void doDispatch(HttpServletRequest request, HttpServletResponse respon
 				if (mappedHandler != null) {
 					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
 				}
+				asyncManager.setMultipartRequestParsed(multipartRequestParsed);
 			}
 			else {
 				// Clean up any resources used by a multipart request.
-				if (multipartRequestParsed) {
+				if (multipartRequestParsed || asyncManager.isMultipartRequestParsed()) {
 					cleanupMultipart(processedRequest);
 				}
 			}