[Java] Preserve serialized ATN version 3 compatibility (#3583)

Author: jcking

runtime/Java/src/org/antlr/v4/runtime/atn/ATNDeserializer.java

@@ -20,10 +20,10 @@
  * @author Sam Harwell
  */
 public class ATNDeserializer {
-	public static final int SERIALIZED_VERSION;
-	static {
-		SERIALIZED_VERSION = 4;
-	}
+
+  static final int LEGACY_SERIALIZED_VERSION = 3;
+
+	public static final int SERIALIZED_VERSION = 4;
 
 	interface UnicodeDeserializer {
 		// Wrapper for readInt() or readInt32()
@@ -90,6 +90,12 @@ public ATN deserialize(char[] data) {
 
 		int p = 0;
 		int version = toInt(data[p++]);
+    if (version == LEGACY_SERIALIZED_VERSION) {
+      // Preserve backwards compatibility for version 3. We simply skip over the UUID and assume all
+      // features were supported.
+      p += 8;
+      version = SERIALIZED_VERSION;
+    }
 		if (version != SERIALIZED_VERSION) {
 			String reason = String.format(Locale.getDefault(), "Could not deserialize ATN with version %d (expected %d).", version, SERIALIZED_VERSION);
 			throw new UnsupportedOperationException(new InvalidClassException(ATN.class.getName(), reason));