[bevy_ui][focus] distinguish mouse buttons

[RostMyr]

What problem does this solve or what need does it fill? ui_focus_system system currently handles only left button clicks/touches. It would be nice to be able to handle right button clicks too.

What solution would you like? Well, probably Interaction::Clicked could be just replaced with Interaction::Clicked(MouseButton) or with Interaction::Clicked(Option<MouseButton>) to handle touches with Option::None 🤷🏻 .