Throw notice on array access on illegal type

Throw notice on array access on illegal type

No notice is thrown for list() accesses, because we did not come
to an agreement regarding patterns like

    while ([$key, $value] = yield $it->next()) { ... }

where silent null access may be desirable.

No effort is made to suppress multiple notices in access chains
likes $x[0][0][0], because the technical complexity this causes
does not seem worthwhile.

RFC: https://wiki.php.net/rfc/notice-for-non-valid-array-container