Support resetting memorizeCurrent for instances like new chat messages

[micahgodbolt]

Right now, we memorize current in copilot chat so that if you tab down into input, but want to tab back up into chat, you don't lose your place.

The problem is that if a new message has been added to chance since you were last there, teams typically want focus to move to that most recent chat item.

defaultFocus only works if there is no memorized focus history, so that only works on the first focus.

https://github.com/microsoft/fluentai/issues/1307

There are also customer scenarios where we simply always want focus to go to the last item, regardless of if there was some saved focus location