[region-isolation] When assigning RValues into memory, use tuple_addr_constructor instead of doing it in pieces.

I also included changes to the rest of the SIL optimizer pipeline to ensure that
the part of the optimizer pipeline before we lower tuple_addr_constructor (which
is right after we run TransferNonSendable) work as before.

The reason why I am doing this is that this ensures that diagnostic passes can
tell the difference in between:

```
x = (a, b, c)
```

and

```
x.0 = a
x.1 = b
x.2 = c
```

This is important for things like TransferNonSendable where assigning over the
entire tuple element is treated differently from if one were to initialize it in
pieces using projections.

rdar://117880194

lib/SILOptimizer/Mandatory/LowerTupleAddrConstructor.cpp

@@ -40,7 +40,7 @@ class LowerTupleAddrConstructorTransform : public SILFunctionTransform {
 
         unsigned count = 0;
         visitExplodedTupleValue(
-            inst->getDestValue(),
+            inst->getDest(),
             [&](SILValue value, std::optional<unsigned> index) -> SILValue {
               if (!index) {
                 SILValue elt = inst->getElement(count);