Make sure WT parser always prepared to accept C1.

src/cascadia/TerminalCore/Terminal.cpp

@@ -61,6 +61,14 @@ Terminal::Terminal() :
 
     _stateMachine = std::make_unique<StateMachine>(std::move(engine));
 
+    // Until we have a true pass-through mode, the decision as to whether C1
+    // controls are interpreted or not is made at the conhost level. If they
+    // are being filtered out, then we will simply never receive them. But if
+    // they are being accepted by conhost, there's a chance they may get passed
+    // through in some situations, so it's important that our state machine is
+    // always prepared to accept them.
+    _stateMachine->SetParserMode(StateMachine::Mode::AcceptC1, true);
+
     auto passAlongInput = [&](std::deque<std::unique_ptr<IInputEvent>>& inEventsToWrite) {
         if (!_pfnWriteInput)
         {