refactor(modal): simplify backdrop creation
refactor(modal): simplify backdrop creation

Closes #5002

burlhock/bootstrap,shootermv/bootstrap,benhalverson/bootstrap,benhalverson/bootstrap,shootermv/bootstrap,deeg/bootstrap,burlhock/bootstrap,caoruiy/bootstrap,vfiles/bootstrap,wesleycho/bootstrap,benhalverson/bootstrap,RobJacobs/bootstrap,byronigoe/bootstrap,mabi/bootstrap,Kpler/bootstrap,benhalverson/bootstrap,shiftagent/ui-bootstrap,fpipita/bootstrap,shiftagent/ui-bootstrap,icfantv/bootstrap,connyay/bootstrap,angular-ui/bootstrap,mabi/bootstrap,Foxandxss/bootstrap,infowrap/bootstrap,caoruiy/bootstrap,RobJacobs/bootstrap,byronigoe/bootstrap,Kpler/bootstrap,angular-ui/bootstrap,christor/bootstrap,christor/bootstrap,looker/bootstrap,infowrap/bootstrap,wesleycho/bootstrap,looker/bootstrap,BookingBug/bootstrap,BookingBug/bootstrap,292388900/bootstrap,Foxandxss/bootstrap,Servoy/bootstrap,Servoy/bootstrap,292388900/bootstrap,fpipita/bootstrap,icfantv/bootstrap,deeg/bootstrap,vfiles/bootstrap,connyay/bootstrap