8336856: Efficient hidden class-based string concatenation strategy

Co-authored-by: Claes Redestad <redestad@openjdk.org>
Reviewed-by: redestad, liach

src/java.base/share/classes/java/lang/System.java

@@ -2623,6 +2623,10 @@ public final class System {
                 return StringConcatHelper.mix(lengthCoder, value);
             }
 
+            public Object stringConcat1(String[] constants) {
+                return new StringConcatHelper.Concat1(constants);
+            }
+
             public int getCharsLatin1(long i, int index, byte[] buf) {
                 return StringLatin1.getChars(i, index, buf);
             }