Update RegisteredClient.Builder to use getters

- Since the class is not final, it is possible to extend it.
  Because the Builder was directly accessing the properties
  rather than using the getters, it was not possible to use
  the .from(id) constructor in the extended class.

Closes gh-451

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/client/RegisteredClient.java

@@ -262,23 +262,23 @@ public class RegisteredClient implements Serializable {
 		}
 
 		protected Builder(RegisteredClient registeredClient) {
-			this.id = registeredClient.id;
-			this.clientId = registeredClient.clientId;
-			this.clientIdIssuedAt = registeredClient.clientIdIssuedAt;
-			this.clientSecret = registeredClient.clientSecret;
-			this.clientSecretExpiresAt = registeredClient.clientSecretExpiresAt;
-			this.clientName = registeredClient.clientName;
-			if (!CollectionUtils.isEmpty(registeredClient.clientAuthenticationMethods)) {
-				this.clientAuthenticationMethods.addAll(registeredClient.clientAuthenticationMethods);
+			this.id = registeredClient.getId();
+			this.clientId = registeredClient.getClientId();
+			this.clientIdIssuedAt = registeredClient.getClientIdIssuedAt();
+			this.clientSecret = registeredClient.getClientSecret();
+			this.clientSecretExpiresAt = registeredClient.getClientSecretExpiresAt();
+			this.clientName = registeredClient.getClientName();
+			if (!CollectionUtils.isEmpty(registeredClient.getClientAuthenticationMethods())) {
+				this.clientAuthenticationMethods.addAll(registeredClient.getClientAuthenticationMethods());
 			}
-			if (!CollectionUtils.isEmpty(registeredClient.authorizationGrantTypes)) {
-				this.authorizationGrantTypes.addAll(registeredClient.authorizationGrantTypes);
+			if (!CollectionUtils.isEmpty(registeredClient.getAuthorizationGrantTypes())) {
+				this.authorizationGrantTypes.addAll(registeredClient.getAuthorizationGrantTypes());
 			}
-			if (!CollectionUtils.isEmpty(registeredClient.redirectUris)) {
-				this.redirectUris.addAll(registeredClient.redirectUris);
+			if (!CollectionUtils.isEmpty(registeredClient.getRedirectUris())) {
+				this.redirectUris.addAll(registeredClient.getRedirectUris());
 			}
-			if (!CollectionUtils.isEmpty(registeredClient.scopes)) {
-				this.scopes.addAll(registeredClient.scopes);
+			if (!CollectionUtils.isEmpty(registeredClient.getScopes())) {
+				this.scopes.addAll(registeredClient.getScopes());
 			}
 			this.clientSettings = ClientSettings.withSettings(registeredClient.getClientSettings().getSettings()).build();
 			this.tokenSettings = TokenSettings.withSettings(registeredClient.getTokenSettings().getSettings()).build();