12.6: Note that finalization may be disabled

For avoidance of confusion, JLS 12.6 should open with an informative note: "As of Java SE 18, the Java SE Platform Specification allows finalization of class instances to be disabled in an Implementation of the Java SE Platform, in anticipation of the removal of finalization from a future release of the Platform."

If finalization continues to be deprecated, but not removed, in Java SE 19, then 12.6's note will have to be updated to say "As of Java SE 19, ...". Only when finalization is removed will 12.6 be struck and references to `finalize` throughout the JLS be removed.

There is no impact on the JVMS, since it does not mention finalization, not even in 2.5.3 which introduces "garbage collector".