Fix High Contrast mode in Settings UI (#18130)

"HighContrast" is not a possible requested theme. So `_UpdateBackgroundForMica()` would force the settings UI to be light or dark. To fix this, we just check if we're in high contrast mode and, if so, we don't bother setting the requested theme.

(cherry picked from commit d04381e)
Service-Card-Id: PVTI_lADOAF3p4s4AmhmQzgUZ6Mc
Service-Version: 1.22

Author: carlos-zamora

src/cascadia/TerminalSettingsEditor/MainPage.cpp

@@ -682,6 +682,12 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
     // can have mica too.
     void MainPage::_UpdateBackgroundForMica()
     {
+        // If we're in high contrast mode, don't override the theme.
+        if (Windows::UI::ViewManagement::AccessibilitySettings accessibilitySettings; accessibilitySettings.HighContrast())
+        {
+            return;
+        }
+
         bool isMicaAvailable = false;
 
         // Check to see if our hosting window supports Mica at all. We'll check

src/cascadia/TerminalSettingsEditor/MainPage.xaml

@@ -44,11 +44,10 @@
                         <ResourceDictionary x:Key="HighContrast">
                             <!--  Define resources for HighContrast mode here  -->
                             <StaticResource x:Key="SettingsPageBackground"
-                                            ResourceKey="SystemColorWindowColorBrush" />
+                                            ResourceKey="SystemColorWindowBrush" />
                             <StaticResource x:Key="SettingsPageMicaBackground"
-                                            ResourceKey="SystemColorWindowColorBrush" />
+                                            ResourceKey="SystemColorWindowBrush" />
                         </ResourceDictionary>
-
                     </ResourceDictionary.ThemeDictionaries>
                 </ResourceDictionary>
 

src/cascadia/TerminalSettingsEditor/pch.h

@@ -31,6 +31,7 @@
 #include <winrt/Windows.UI.Input.h>
 #include <winrt/Windows.UI.Popups.h>
 #include <winrt/Windows.UI.Text.h>
+#include <winrt/Windows.UI.ViewManagement.h>
 #include <winrt/Windows.UI.Xaml.h>
 #include <winrt/Windows.UI.Xaml.Automation.h>
 #include <winrt/Windows.UI.Xaml.Automation.Peers.h>