Scroll to top when select all action is invoked (#13656)

## Summary of the Pull Request
In general, when a selection marker is shown, we should scroll to it. The `selectAll` action adds a selection marker, but we don't scroll to it. This PR makes it such that we do do that.

Epic: #4993 
Closes #13485

src/cascadia/TerminalCore/TerminalSelection.cpp

@@ -625,6 +625,7 @@ void Terminal::SelectAll()
     _selection->end = { bufferSize.RightInclusive(), _GetMutableViewport().BottomInclusive() };
     _selection->pivot = _selection->end;
     _selectionMode = SelectionInteractionMode::Keyboard;
+    _ScrollToPoint(_selection->start);
 }
 
 void Terminal::_MoveByChar(SelectionDirection direction, til::point& pos)