[ConstraintSystem] Detect and fix extraneous use of &

Diagnose extraneous use of address of (`&`) which could only be
associated with arguments to `inout` parameters e.g.

```swift
struct S {}

var a: S = ...
var b: S = ...

a = &b
```

lib/Sema/CSDiagnostics.cpp

@@ -2674,3 +2674,9 @@ bool InvalidMethodRefInKeyPath::diagnoseAsError() {
                  getName(), isForKeyPathDynamicMemberLookup());
   return true;
 }
+
+bool InvalidUseOfAddressOf::diagnoseAsError() {
+  auto *anchor = cast<AssignExpr>(getAnchor());
+  emitDiagnostic(anchor->getSrc()->getLoc(), diag::extraneous_address_of);
+  return true;
+}