Since PHP 7.4 objects that have a destructor require two GC runs
to be collected. Currently the collection is delayed to the next
automatic GC run. However, in some cases this may result in a large
increase in memory usage, as in one of the cases of bug #79519.
See also bug #78933 and bug #81117 where the current behavior is
unexpected for users.
This patch will automatically rerun GC if destructors were encountered.
I think this should not have much cost, because it is very likely that
objects on which the destructor has been called really are garbage,
so the extra GC run should not be doing wasted work.
Closes GH-5581.
For objects with destructors, we will now only call the destructor
in the initial GC run, and remove any nested data. The object is
marked purple so it will be considered a root for the next GC run,
at which point it will be fully destroyed, if possible.
GC counts change on a number of tests, as the objects now get
destroyed later.
