Fix PGO on 1.26 by disabling part of Per-Window Settings (#20751)

See #20749 for more info.

This is a version of #20750 targeting the 1.26 release branch so that we
can actually do a PGO run.

I believe this is safe to remove because it was introduced to address a
theme difference in the Settings UI when it moved between windows with
different themes. The Settings UI is given the theme during
construction, so that's the only explanation I can think of for why it's
like this.

src/cascadia/TerminalApp/TabManagement.cpp

@@ -102,11 +102,13 @@ namespace winrt::TerminalApp::implementation
     {
         newTabImpl->Initialize();
 
+#ifdef CODE_DISABLED_PER_WINDOW_SETTINGS // See GH#20749.
         // Push the current settings into the tab on when it's initialized.
         // _RefreshUIForSettingsReload will also do this when settings are hot
         // reloaded, but we need this here to make sure we pass our current
         // window settings to the tab too.
         newTabImpl->UpdateSettings(_settings, _currentWindowSettings());
+#endif
 
         // If insert position is not passed, calculate it
         if (insertPosition == -1)