Add a confirmation dialog for "Close Other Tabs" contextual menu action

[bsclifton]

Carried over from brave/browser-laptop#1382

This action is not undoable and can be triggered accidentally.

Users can undo closed tabs, I think a dialog would be a tad annoying here. One other data point is that there is no confirmation in Chrome.

It would be useful if you had more then 20 that would be closed all at once. And a data point - we are better than chrome. : )