Send focus events even in ReadOnly mode (#13483)

Does what it says on the tin. When we get focused, temporarily turn off readonly mode, as to not pop the dialog when the focus sequence is eventually sent to the connection.

* closes #13461

(cherry picked from commit b4a52c8)
Service-Card-Id: 84111371
Service-Version: 1.15

src/cascadia/TerminalControl/ControlCore.cpp

@@ -1912,13 +1912,24 @@ namespace winrt::Microsoft::Terminal::Control::implementation
     // - This is related to work done for GH#2988.
     void ControlCore::GotFocus()
     {
-        _terminal->FocusChanged(true);
+        _focusChanged(true);
     }
 
     // See GotFocus.
     void ControlCore::LostFocus()
     {
-        _terminal->FocusChanged(false);
+        _focusChanged(false);
+    }
+
+    void ControlCore::_focusChanged(bool focused)
+    {
+        // GH#13461 - temporarily turn off read-only mode, send the focus event,
+        // then turn it back on. Even in focus mode, focus events are fine to
+        // send. We don't want to pop a warning every time the control is
+        // focused.
+        const auto previous = std::exchange(_isReadOnly, false);
+        const auto restore = wil::scope_exit([&]() { _isReadOnly = previous; });
+        _terminal->FocusChanged(focused);
     }
 
     bool ControlCore::_isBackgroundTransparent()

src/cascadia/TerminalControl/ControlCore.h

@@ -311,6 +311,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         void _setOpacity(const double opacity);
 
         bool _isBackgroundTransparent();
+        void _focusChanged(bool focused);
 
         inline bool _IsClosing() const noexcept
         {