Allow file modifications to quiet down before reloading settings (#1330)

This commit introduces a 50ms debounce so that we stop flapping around while text editors are making directory changes.

Fixes #1329.

src/cascadia/TerminalApp/App.cpp

@@ -595,11 +595,26 @@ namespace winrt::TerminalApp::implementation
 
                            if (settingsBasename == modifiedBasename)
                            {
-                               this->_ReloadSettings();
+                               this->_DispatchReloadSettings();
                            }
                        });
     }
 
+    // Method Description:
+    // - Dispatches a settings reload with debounce.
+    //   Text editors implement Save in a bunch of different ways, so
+    //   this stops us from reloading too many times or too quickly.
+    fire_and_forget App::_DispatchReloadSettings()
+    {
+        static constexpr auto FileActivityQuiesceTime{ std::chrono::milliseconds(50) };
+        if (!_settingsReloadQueued.exchange(true))
+        {
+            co_await winrt::resume_after(FileActivityQuiesceTime);
+            _ReloadSettings();
+            _settingsReloadQueued.store(false);
+        }
+    }
+
     // Method Description:
     // - Reloads the settings from the profile.json.
     void App::_ReloadSettings()

src/cascadia/TerminalApp/App.h

@@ -69,6 +69,8 @@ namespace winrt::TerminalApp::implementation
 
         wil::unique_folder_change_reader_nothrow _reader;
 
+        std::atomic<bool> _settingsReloadQueued{ false };
+
         void _Create();
         void _CreateNewTabFlyout();
 
@@ -85,6 +87,7 @@ namespace winrt::TerminalApp::implementation
         void _HookupKeyBindings(TerminalApp::AppKeyBindings bindings) noexcept;
 
         void _RegisterSettingsChange();
+        fire_and_forget _DispatchReloadSettings();
         void _ReloadSettings();
 
         void _SettingsButtonOnClick(const IInspectable& sender, const Windows::UI::Xaml::RoutedEventArgs& eventArgs);