Make TokenType constructor public

Closes gh-16086

oauth2/oauth2-core/src/main/java/org/springframework/security/oauth2/core/OAuth2AccessToken.java

@@ -114,7 +114,12 @@ public class OAuth2AccessToken extends AbstractOAuth2Token {
 
 		private final String value;
 
-		private TokenType(String value) {
+		/**
+		 * Constructs a {@code TokenType} using the provided value.
+		 * @param value the value of the token type
+		 * @since 6.5
+		 */
+		public TokenType(String value) {
 			Assert.hasText(value, "value cannot be empty");
 			this.value = value;
 		}