Apply StringUtils.cleanPath for Windows path compatibility

See gh-28006

Author: jhoeller

spring-web/src/main/java/org/springframework/http/codec/multipart/FilePartEvent.java

@@ -125,7 +125,7 @@ static Flux<FilePartEvent> create(String name, Path path, @Nullable Consumer<Htt
 		Assert.notNull(path, "Path must not be null");
 
 		return Flux.defer(() -> {
-			String pathName = path.toString();
+			String pathName = StringUtils.cleanPath(path.toString());
 			MediaType contentType = MediaTypeFactory.getMediaType(pathName)
 					.orElse(MediaType.APPLICATION_OCTET_STREAM);
 			String filename = StringUtils.getFilename(pathName);