8247: Custom key bindings are broken for tab navigation (#8250)

There are two code paths for Ctrl+Tab and for everything else:

Ctrl + Tab is working perfectly
* On the first tab navigation TerminalPage::_SelectNextTab resets the
  tab commands, and since palette is not visible selects the relevant
  tab index
* On the second navigation Ctrl+Tab is intercepted by
  CommandPalette::_previewKeyDownHandler and everything works fine

But with custom binding things are screwed:
* On the first tab navigation TerminalPage::_SelectNextTab resets the
  tab commands, and since palette is not visible selects the relevant
  tab index
* On the second navigation keys are not intercepted and thus
  TerminalPage::_SelectNextTab is called again. It resets the commands,
  but now since the palette is visible we simply invoke
  CommandPalette::SelectNextItem. Which in turn misbehaves because no
  item is selected.

The approach for the solution is not to reset anything if the command
palette is already open.

* Manual testing of both custom and non-custom bindings with different
  amount of tabs.

Closes #8247

(cherry picked from commit 0437fe9)

Author: Don-Vito

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -1218,6 +1218,14 @@ namespace winrt::TerminalApp::implementation
     // - Sets focus to the tab to the right or left the currently selected tab.
     void TerminalPage::_SelectNextTab(const bool bMoveRight)
     {
+        if (CommandPalette().Visibility() == Visibility::Visible)
+        {
+            // If the tab switcher is currently open, don't change its mode.
+            // Just select the new tab.
+            CommandPalette().SelectNextItem(bMoveRight);
+            return;
+        }
+
         if (_settings.GlobalSettings().UseTabSwitcher())
         {
             CommandPalette().SetTabActions(_mruTabActions);
@@ -1227,15 +1235,10 @@ namespace winrt::TerminalApp::implementation
             uint32_t tabCount = _mruTabActions.Size();
             auto newTabIndex = ((tabCount + (bMoveRight ? 1 : -1)) % tabCount);
 
-            if (CommandPalette().Visibility() == Visibility::Visible)
-            {
-                CommandPalette().SelectNextItem(bMoveRight);
-            }
-            else
-            {
-                CommandPalette().EnableTabSwitcherMode(false, newTabIndex);
-                CommandPalette().Visibility(Visibility::Visible);
-            }
+            // Otherwise, set up the tab switcher in the selected mode, with
+            // the given ordering, and make it visible.
+            CommandPalette().EnableTabSwitcherMode(false, newTabIndex);
+            CommandPalette().Visibility(Visibility::Visible);
         }
         else if (auto index{ _GetFocusedTabIndex() })
         {