[ownership] Add a new helper InteriorPointerOperand::getSingleBaseValue().
[ownership] Add a new helper InteriorPointerOperand::getSingleBaseValue().

This returns the underlying BorrowedValue that introduce's the interior pointer
operand's associated value.

gregomni/swift,hooman/swift,tkremenek/swift,benlangmuir/swift,tkremenek/swift,gregomni/swift,JGiola/swift,glessard/swift,rudkx/swift,xwu/swift,benlangmuir/swift,hooman/swift,hooman/swift,glessard/swift,ahoppen/swift,JGiola/swift,roambotics/swift,rudkx/swift,parkera/swift,atrick/swift,gregomni/swift,glessard/swift,roambotics/swift,ahoppen/swift,rudkx/swift,JGiola/swift,JGiola/swift,ahoppen/swift,benlangmuir/swift,atrick/swift,parkera/swift,ahoppen/swift,benlangmuir/swift,gregomni/swift,JGiola/swift,apple/swift,xwu/swift,ahoppen/swift,tkremenek/swift,hooman/swift,rudkx/swift,rudkx/swift,xwu/swift,atrick/swift,parkera/swift,benlangmuir/swift,apple/swift,gregomni/swift,atrick/swift,tkremenek/swift,atrick/swift,atrick/swift,roambotics/swift,hooman/swift,benlangmuir/swift,roambotics/swift,glessard/swift,xwu/swift,parkera/swift,hooman/swift,rudkx/swift,apple/swift,apple/swift,apple/swift,hooman/swift,parkera/swift,parkera/swift,apple/swift,JGiola/swift,parkera/swift,xwu/swift,roambotics/swift,tkremenek/swift,tkremenek/swift,parkera/swift,gregomni/swift,tkremenek/swift,xwu/swift,xwu/swift,roambotics/swift,glessard/swift,ahoppen/swift,glessard/swift