Prevent tab reordering while elevated

There's a platform limitation that causes us to crash when we rearrange
tabs. Xaml tries to send a drag visual (to wit: a screenshot) to the
drag hosting process, but that process is running at a different IL than
us.

For now, we're disabling elevated drag.

Fixes #3581

src/cascadia/TerminalApp/AppLogic.cpp

@@ -115,6 +115,27 @@ static Documents::Run _BuildErrorRun(const winrt::hstring& text, const ResourceD
     return textRun;
 }
 
+// Method Description:
+// - Returns whether the user is either a member of the Administrators group or
+//   is currently elevated.
+// Return Value:
+// - true if the user is an administrator
+static bool _isUserAdmin() noexcept
+try
+{
+    SID_IDENTIFIER_AUTHORITY ntAuthority{ SECURITY_NT_AUTHORITY };
+    wil::unique_sid adminGroupSid{};
+    THROW_IF_WIN32_BOOL_FALSE(AllocateAndInitializeSid(&ntAuthority, 2, SECURITY_BUILTIN_DOMAIN_RID, DOMAIN_ALIAS_RID_ADMINS, 0, 0, 0, 0, 0, 0, &adminGroupSid));
+    BOOL b;
+    THROW_IF_WIN32_BOOL_FALSE(CheckTokenMembership(NULL, adminGroupSid.get(), &b));
+    return !!b;
+}
+catch (...)
+{
+    LOG_CAUGHT_EXCEPTION();
+    return false;
+}
+
 namespace winrt::TerminalApp::implementation
 {
     AppLogic::AppLogic() :
@@ -131,6 +152,7 @@ namespace winrt::TerminalApp::implementation
         // The TerminalPage has to be constructed during our construction, to
         // make sure that there's a terminal page for callers of
         // SetTitleBarContent
+        _isElevated = _isUserAdmin();
         _root = winrt::make_self<TerminalPage>();
     }
 
@@ -145,6 +167,17 @@ namespace winrt::TerminalApp::implementation
         return _isUwp;
     }
 
+    // Method Description:
+    // - Called around the codebase to discover if Terminal is running elevated
+    // Arguments:
+    // - <none> - reports internal state
+    // Return Value:
+    // - True if elevated, false otherwise.
+    bool AppLogic::IsElevated() const noexcept
+    {
+        return _isElevated;
+    }
+
     // Method Description:
     // - Called by UWP context invoker to let us know that we may have to change some of our behaviors
     //   for being a UWP

src/cascadia/TerminalApp/AppLogic.h

@@ -21,6 +21,7 @@ namespace winrt::TerminalApp::implementation
         void Create();
         bool IsUwp() const noexcept;
         void RunAsUwp();
+        bool IsElevated() const noexcept;
         void LoadSettings();
         [[nodiscard]] std::shared_ptr<::TerminalApp::CascadiaSettings> GetSettings() const noexcept;
 
@@ -47,6 +48,7 @@ namespace winrt::TerminalApp::implementation
 
     private:
         bool _isUwp{ false };
+        bool _isElevated{ false };
 
         // If you add controls here, but forget to null them either here or in
         // the ctor, you're going to have a bad time. It'll mysteriously fail to

src/cascadia/TerminalApp/AppLogic.idl

@@ -25,6 +25,7 @@ namespace TerminalApp
 
         Boolean IsUwp();
         void RunAsUwp();
+        Boolean IsElevated();
 
         Int32 SetStartupCommandline(String[] commands);
         String EarlyExitMessage { get; };

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -63,6 +63,14 @@ namespace winrt::TerminalApp::implementation
         _tabView = _tabRow.TabView();
         _rearranging = false;
 
+        // GH#3581 - There's a platform limitation that causes us to crash when we rearrange tabs.
+        // Xaml tries to send a drag visual (to wit: a screenshot) to the drag hosting process,
+        // but that process is running at a different IL than us.
+        // For now, we're disabling elevated drag.
+        const auto isElevated = ::winrt::Windows::UI::Xaml::Application::Current().as<::winrt::TerminalApp::App>().Logic().IsElevated();
+        _tabView.CanReorderTabs(!isElevated);
+        _tabView.CanDragTabs(!isElevated);
+
         _tabView.TabDragStarting([weakThis{ get_weak() }](auto&& /*o*/, auto&& /*a*/) {
             if (auto page{ weakThis.get() })
             {