Fix ZTS build
Switch ai accessors from members to array

The accessors are now accessed via ->fn[ZEND_ACCESSOR_GET] rather than
->getter.

This allows us to simply loop through the accessors functions, rather than
always handling them individually. It also allows to write generic functions
that work on all accessors.

This also fixes Reflection to properly take into account ->isset and ->unset
which were previously ignored to the most part.