Use HttpMethod::valueOf in HttpMethod::resolve

This commit makes sure that HttpMethod::resolve uses HttpMethod::valueOf
and returns an HttpMethod for non-standard methods.

See gh-27697

Author: poutsma

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

@@ -146,7 +146,7 @@ public static HttpMethod valueOf(String method) {
 	@Nullable
 	@Deprecated
 	public static HttpMethod resolve(@Nullable String method) {
-		return (method != null ? mappings.get(method) : null);
+		return (method != null ? valueOf(method) : null);
 	}