Allow overriding border runes per instance of Box

Borders of focused elements are drawn differently than for unfocused ones (thicker / double lines).

Would be nice if there is a method to control that behavior. While it's possible to override the runes that are used for focused elements globally, one might want to have this for specific boxes/containers only.

The only way to work around it is to use SetDrawFunc and draw the borders yourself I guess?

I'm thinking about a boolean like borderIgnoreFocus added to the Box struct with a method SetBorderIgnoreFocus(ignore bool) which can then be checked in the DrawForSubclass

https://github.com/rivo/tview/issues/747#issuecomment-1198967978