Dismiss Terminal-by-default banner on handoff (#13344)

It's not useful to notify users that WT can be made the default if it's already
clearly being used for handoff. This commit will suppresses the banner then.

## PR Checklist
* [x] Closes #13314
* [x] I work here

## Validation Steps Performed
* Modify `TerminalPage::ShowSetAsDefaultInfoBar` to not check for
  `CascadiaSettings::IsDefaultTerminalSet()`
* Set Terminal Dev as the default
* Set incoming connections to open in the latest Terminal window
* Delete `state.json` after every test below
* Launching Terminal Dev shows the banner ✅
  Launching `cmd.exe` dismisses the banner in the current Terminal ✅
* Launching `cmd.exe` launches Terminal Dev without banner ✅

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -3274,6 +3274,9 @@ namespace winrt::TerminalApp::implementation
 
             // Request a summon of this window to the foreground
             _SummonWindowRequestedHandlers(*this, nullptr);
+
+            const IInspectable unused{ nullptr };
+            _SetAsDefaultDismissHandler(unused, unused);
             return S_OK;
         }
         CATCH_RETURN()