8205626: Start of release updates for JDK 13

8205393: Add SourceVersion.RELEASE_13
8205394: Add source 13 and target 13 to javac
8205645: Bump maximum recognized class file version to 57 for JDK 13
8214825: Update preview language features for start of JDK 13

Reviewed-by: erikj, alanb, mchung, mcimadamore, dholmes, smarks, jjg

test/langtools/tools/javac/classfiles/ClassVersionChecker.java

@@ -47,7 +47,8 @@ public class ClassVersionChecker {
         NINE("9", 53),
         TEN("10", 54),
         ELEVEN("11", 55),
-        TWELVE("12", 56);
+        TWELVE("12", 56),
+        THIRTEEN("13", 57);
 
         private Version(String release, int classFileVer) {
             this.release = release;