[AddressLowering] Handle guaranteed destructures.
Previously, when lowering destructure_tuple and destructure_struct
instructions, either a load [trivial] or load [take] was always created
for each loadable field. When the operand to the destructure
instruction was @owned, this was the correct behavior; but when the
operand was @guaranteed, it was not. It would result in SIL like
```
(..., %elt_addr, ...) = destructure_ %addr
%value = load [take] %elt_addr
destroy_addr %addr
```
where (1) %elt_addr was destroyed twice (once by the load [take] and
once by the destroy_addr of the aggregate and (2) the loaded value was
leaked.
Here, this is fixed by creating load_borrows for this case.
