With the GC heap conversion, the functionality of legacy platform
objects was broken. This is because the generated implementation of one
of them was used for all of them, removing functionality such as
deletion.
This re-adds all functionality, where questions such as "does the
object support indexed properties?" is instead answered by virtual
functions instead of by the IDL generator checking the presence of
certain keywords/attributes.
Note that as of this commit, there aren't any such throwers, and the
call site in Heap::allocate will drop exceptions on the floor. This
commit only serves to change the declaration of the overrides, make sure
they return an empty value, and to propagate OOM errors frm their base
initialize invocations.
