Stash HWND things

I was starting to port over the focus & show/hide & reparent things from #2988, but this isn't it. I know sufficiently little about how this works, that I won't be able to do this. Additionally, we don't own the actual WPF conpty connection (VS does), so I can't just implement it here.

src/cascadia/PublicTerminalCore/HwndTerminal.cpp

@@ -836,12 +836,14 @@ void __stdcall TerminalSetFocus(void* terminal)
 {
     auto publicTerminal = static_cast<HwndTerminal*>(terminal);
     publicTerminal->_focused = true;
+    // TODO!: somehow let the core terminal know about focus events?
 }
 
 void __stdcall TerminalKillFocus(void* terminal)
 {
     auto publicTerminal = static_cast<HwndTerminal*>(terminal);
     publicTerminal->_focused = false;
+    // TODO!: somehow let the core terminal know about focus events?
 }
 
 // Routine Description:

src/cascadia/TerminalConnection/ConptyConnection.idl

@@ -7,18 +7,15 @@ namespace Microsoft.Terminal.TerminalConnection
 {
     delegate void NewConnectionHandler(ConptyConnection connection);
 
-    [default_interface] runtimeclass ConptyConnection : ITerminalConnection
+    [default_interface] runtimeclass ConptyConnection : ITerminalConnection,
+                                                        IWindowHostedConnection
     {
         ConptyConnection();
         Guid Guid { get; };
         String Commandline { get; };
 
         void ClearBuffer();
 
-        void ShowHide(Boolean show);
-
-        void ReparentWindow(UInt64 newParent);
-
         static event NewConnectionHandler NewConnection;
         static void StartInboundListener();
         static void StopInboundListener();

src/cascadia/TerminalConnection/ITerminalConnection.idl

@@ -29,4 +29,10 @@ namespace Microsoft.Terminal.TerminalConnection
         event Windows.Foundation.TypedEventHandler<ITerminalConnection, Object> StateChanged;
         ConnectionState State { get; };
     };
+
+    interface IWindowHostedConnection
+    {
+        void ShowHide(Boolean show);
+        void ReparentWindow(UInt64 newParent);
+    };
 }

src/cascadia/WpfTerminalControl/IWindowHostedConnection.cs

@@ -12,6 +12,9 @@ namespace Microsoft.Terminal.Wpf
     /// </summary>
     public interface IWindowHostedConnection
     {
+
+        void ShowHide(bool show);
+
         /// <summary>
         /// Inform the connection that the HWND we are hosted in has changed.
         /// </summary>

src/cascadia/WpfTerminalTestNetCore/MainWindow.xaml.cs

@@ -15,7 +15,7 @@
 
 namespace WpfTerminalTestNetCore
 {
-    public class EchoConnection : Microsoft.Terminal.Wpf.ITerminalConnection
+    public class EchoConnection : Microsoft.Terminal.Wpf.ITerminalConnection, Microsoft.Terminal.Wpf.IWindowHostedConnection
     {
         public event EventHandler<TerminalOutputEventArgs> TerminalOutput;