[php-src] Issue #7825: Add nullsafe call and index access

Issue: https://github.com/php/php-src/issues/7825 Author: Vovan-VE ### Description ### Proposal ```php // Nullsafe call $res = $optionalClosure?->(1, 2, 3); $res = ($obj->optionalClosure)?->(1, 2, 3); // or even? $res = $obj->optionalClosure?->(1, 2, 3); // Nullsafe index access $res = $optionalArray?->[42]; $res = $obj->optionalArray?->[42]; ``` ### Backward Incompatible Changes No. ### Motivation 1. Nullsafe access operator ?-> already exists and whole expression consists of existing tokens only; 2. Syntax like $fn?() and $arr?[42] is not possible since it's a part of already valid syntax ?: ; 3. Syntax like $fn?‗() and $arr?‗[42] (where ‗ is anything else) most probably will never be added because ‗ is literally something else and leads to inconsistency with $obj?->member. ### Open Issues * Must $obj->optionalClosure require parentheses ($obj->optionalClosure)?->() like ($obj->closure)() does? ### Future Scope Probably it may be a small step forward to $array->methods() like [1,2,3]->map(fn ($x) => $x * 10) which itself may be a step to more features like (-42)->abs(), $str->trim()->replace(...)->replace(...).