In OSSA, the `partial_apply [on_stack]` instruction produces a value
with odd characteristics that correspond to the fact that it is lowered
to a stack-allocating instruction. Among these characteristics is the
fact that copies of such values aren't load bearing.
When visiting the lifetime-ending uses of a `partial_apply [on_stack]`
the lifetime ending uses of (transitive) copies of the partial_apply
must be considered as well. Otherwise, the borrow scope it defins may be
incorrectly short:
```
%closure = partial_apply %fn(%value) // borrows %value
%closure2 = copy_value %closure
destroy_value %closure // does _not_ end borrow of %value!
...
destroy_value %closure2 // ends borrow of %value
...
destroy_value %value
```
Furthermore, _only_ the final such destroys actually count as the real
lifetime ends. At least one client (OME) relies on
`visitOnStackLifetimeEnds` visiting at most a single lifetime end on any
path.
Rewrite the utility to use PrunedLiveness, tracking only destroys of
copies and forwards. The final destroys are the destroys on the
boundary.
rdar://142636711
