Make OAuth2AuthorizationResponseType constructor public

Closes gh-9584

oauth2/oauth2-core/src/main/java/org/springframework/security/oauth2/core/endpoint/OAuth2AuthorizationResponseType.java

@@ -56,7 +56,7 @@ public final class OAuth2AuthorizationResponseType implements Serializable {
 
 	private final String value;
 
-	private OAuth2AuthorizationResponseType(String value) {
+	public OAuth2AuthorizationResponseType(String value) {
 		Assert.hasText(value, "value cannot be empty");
 		this.value = value;
 	}