Support php 8.0's nullsafe operator (?->)

[TysonAndre]

https://wiki.php.net/rfc/nullsafe_operator

   $foo = $a?->b();
// --------------- chain 1
//        -------- chain 2
// If $a is null chain 2 is aborted, method b() isn't called, null is assigned to $foo
 
   $a?->b($c->d());
// --------------- chain 1
//        -------  chain 2
// If $a is null chain 1 is aborted, method b() isn't called, the expression `$c->d()` is not evaluated
 
   $a->b($c?->d());
// --------------- chain 1
//       --------  chain 2
// If $c is null chain 2 is aborted, method d() isn't called, null is passed to `$a->b()`

This appears to be straightforward - T_NULLSAFE_OBJECT_OPERATOR looks to have the same precedence and places it can occur as T_OBJECT_OPERATOR(->)