Avoid writing content-length twice in resource handling

Prior to this commit, the `ResourceHttpRequestHandler` would write the
resource size to the "Content-Length" response header.
This is already done by the underlying `ResourceHttpMessageConverter`
and `ResourceRegionHttpMessageConverter`.

This commit avoid this duplicate operation and delegates instead to the
converters.

See gh-26330
Closes gh-26340

Author: paulcwarren

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceHttpRequestHandler.java

@@ -759,14 +759,6 @@ protected MediaType getMediaType(HttpServletRequest request, Resource resource)
 	protected void setHeaders(HttpServletResponse response, Resource resource, @Nullable MediaType mediaType)
 			throws IOException {
 
-		long length = resource.contentLength();
-		if (length > Integer.MAX_VALUE) {
-			response.setContentLengthLong(length);
-		}
-		else {
-			response.setContentLength((int) length);
-		}
-
 		if (mediaType != null) {
 			response.setContentType(mediaType.toString());
 		}