Merge #13769: Mark single-argument constructors "explicit"

1ac3c983bf Mark single-argument constructors "explicit" (practicalswift)

Pull request description:

  Mark single-argument constructors `explicit`.

  Rationale:
  * Avoid unexpected implicit promotions.

  From the developer notes:

  > **By default, declare single-argument constructors explicit.**
  > Rationale: This is a precaution to avoid unintended conversions that might arise when single-argument constructors are used as implicit conversion functions.

Tree-SHA512: 7901ed5be808c9d0ecb5ca501e1bc0395987fe1b7941b8548cebac2ff08a14f7dab61fab374a69b9ba29a9295a04245c814325c7f95b97ae558af0780f111dfa

src/qt/transactiontablemodel.cpp

@@ -60,7 +60,7 @@ struct TxLessThan
 class TransactionTablePriv
 {
 public:
-    TransactionTablePriv(TransactionTableModel *_parent) :
+    explicit TransactionTablePriv(TransactionTableModel *_parent) :
         parent(_parent)
     {
     }