For active !MenuBars, open and close submenus immediately.   I.E. even if the previously hovered/focused !MenuBarItem didn't have a menu, show the menu for the new !PopupBarMenu immediately.   And conversely, even if the new !MenuBarItem doesn't have a menu, close the old menu immediately.  Fixes #10721 !strict.

Also converted _markActive(), _markInactive(), and isActive flag to standard "activated" property with custom setter.   Didn't call it "active" because that's already used by _CssStateMixin.