[Evaluator] Fix an egregious bug in move construction/assignment of AnyRequest

The default move constructor and move assignment operator of AnyRequest
would leave the source object in an odd state that’s destructible but
does not maintain the invariant that all “normal” states store a real
instance. This state breaks DenseMap, which assumes that a moved-from
object is still washable.

Author: DougGregor

include/swift/AST/AnyRequest.h

@@ -136,9 +136,20 @@ class AnyRequest {
 
 public:
   AnyRequest(const AnyRequest &other) = default;
-  AnyRequest(AnyRequest &&other) = default;
   AnyRequest &operator=(const AnyRequest &other) = default;
-  AnyRequest &operator=(AnyRequest &&other) = default;
+
+  AnyRequest(AnyRequest &&other)
+      : storageKind(other.storageKind), stored(std::move(other.stored)) {
+    other.storageKind = StorageKind::Empty;
+  }
+
+  AnyRequest &operator=(AnyRequest &&other) {
+    storageKind = other.storageKind;
+    stored = std::move(other.stored);
+    other.storageKind = StorageKind::Empty;
+    other.stored = nullptr;
+    return *this;
+  }
 
   AnyRequest(AnyRequest &other)
     : storageKind(other.storageKind), stored(other.stored) { }