Add a test case that exercises opaque existential box's value witness assignWith
Add a test case that exercises opaque existential box's value witness assignWith

rdar://31955457

shajrawi/swift,djwbrown/swift,aschwaighofer/swift,harlanhaskins/swift,austinzheng/swift,JGiola/swift,benlangmuir/swift,gregomni/swift,alblue/swift,roambotics/swift,natecook1000/swift,uasys/swift,ahoppen/swift,sschiau/swift,deyton/swift,shajrawi/swift,uasys/swift,CodaFi/swift,felix91gr/swift,deyton/swift,natecook1000/swift,tjw/swift,glessard/swift,sschiau/swift,amraboelela/swift,shahmishal/swift,gregomni/swift,jckarter/swift,return/swift,hooman/swift,gregomni/swift,atrick/swift,huonw/swift,xwu/swift,sschiau/swift,airspeedswift/swift,zisko/swift,harlanhaskins/swift,return/swift,swiftix/swift,hughbe/swift,benlangmuir/swift,benlangmuir/swift,airspeedswift/swift,karwa/swift,allevato/swift,uasys/swift,JGiola/swift,OscarSwanros/swift,danielmartin/swift,glessard/swift,djwbrown/swift,lorentey/swift,austinzheng/swift,lorentey/swift,xedin/swift,shajrawi/swift,jopamer/swift,devincoughlin/swift,deyton/swift,stephentyrone/swift,calebd/swift,return/swift,lorentey/swift,practicalswift/swift,jtbandes/swift,uasys/swift,CodaFi/swift,djwbrown/swift,allevato/swift,gribozavr/swift,devincoughlin/swift,shajrawi/swift,practicalswift/swift,return/swift,shahmishal/swift,apple/swift,djwbrown/swift,jmgc/swift,stephentyrone/swift,hughbe/swift,jtbandes/swift,brentdax/swift,OscarSwanros/swift,brentdax/swift,airspeedswift/swift,swiftix/swift,atrick/swift,xedin/swift,frootloops/swift,nathawes/swift,aschwaighofer/swift,aschwaighofer/swift,swiftix/swift,amraboelela/swift,atrick/swift,Jnosh/swift,ahoppen/swift,parkera/swift,alblue/swift,ahoppen/swift,karwa/swift,swiftix/swift,deyton/swift,milseman/swift,tkremenek/swift,jtbandes/swift,stephentyrone/swift,deyton/swift,brentdax/swift,jmgc/swift,felix91gr/swift,stephentyrone/swift,allevato/swift,huonw/swift,roambotics/swift,felix91gr/swift,tkremenek/swift,jckarter/swift,hughbe/swift,apple/swift,OscarSwanros/swift,rudkx/swift,aschwaighofer/swift,gribozavr/swift,xwu/swift,gregomni/swift,gregomni/swift,shahmishal/swift,OscarSwanros/swift,natecook1000/swift,amraboelela/swift,ahoppen/swift,jmgc/swift,hooman/swift,glessard/swift,alblue/swift,shajrawi/swift,lorentey/swift,hooman/swift,aschwaighofer/swift,shajrawi/swift,amraboelela/swift,stephentyrone/swift,zisko/swift,calebd/swift,frootloops/swift,deyton/swift,benlangmuir/swift,gribozavr/swift,JGiola/swift,gribozavr/swift,JGiola/swift,harlanhaskins/swift,roambotics/swift,glessard/swift,Jnosh/swift,apple/swift,brentdax/swift,huonw/swift,sschiau/swift,airspeedswift/swift,milseman/swift,danielmartin/swift,rudkx/swift,nathawes/swift,shahmishal/swift,danielmartin/swift,devincoughlin/swift,shahmishal/swift,devincoughlin/swift,hooman/swift,jopamer/swift,sschiau/swift,stephentyrone/swift,calebd/swift,karwa/swift,airspeedswift/swift,alblue/swift,felix91gr/swift,xedin/swift,djwbrown/swift,jckarter/swift,gribozavr/swift,jtbandes/swift,tkremenek/swift,xedin/swift,lorentey/swift,practicalswift/swift,austinzheng/swift,xwu/swift,natecook1000/swift,nathawes/swift,alblue/swift,ahoppen/swift,stephentyrone/swift,danielmartin/swift,felix91gr/swift,harlanhaskins/swift,airspeedswift/swift,tjw/swift,xwu/swift,roambotics/swift,jmgc/swift,practicalswift/swift,calebd/swift,nathawes/swift,karwa/swift,xedin/swift,hooman/swift,parkera/swift,tkremenek/swift,nathawes/swift,brentdax/swift,glessard/swift,CodaFi/swift,harlanhaskins/swift,jckarter/swift,devincoughlin/swift,jopamer/swift,atrick/swift,natecook1000/swift,zisko/swift,OscarSwanros/swift,austinzheng/swift,karwa/swift,milseman/swift,Jnosh/swift,harlanhaskins/swift,devincoughlin/swift,parkera/swift,ahoppen/swift,hughbe/swift,uasys/swift,jopamer/swift,alblue/swift,airspeedswift/swift,frootloops/swift,JGiola/swift,xwu/swift,zisko/swift,rudkx/swift,uasys/swift,shajrawi/swift,Jnosh/swift,parkera/swift,atrick/swift,jmgc/swift,natecook1000/swift,tjw/swift,brentdax/swift,jmgc/swift,gribozavr/swift,allevato/swift,lorentey/swift,milseman/swift,parkera/swift,devincoughlin/swift,Jnosh/swift,nathawes/swift,zisko/swift,shahmishal/swift,swiftix/swift,jtbandes/swift,calebd/swift,sschiau/swift,gribozavr/swift,jckarter/swift,jckarter/swift,sschiau/swift,xedin/swift,frootloops/swift,rudkx/swift,gregomni/swift,karwa/swift,allevato/swift,aschwaighofer/swift,djwbrown/swift,practicalswift/swift,danielmartin/swift,harlanhaskins/swift,austinzheng/swift,OscarSwanros/swift,apple/swift,hughbe/swift,return/swift,atrick/swift,benlangmuir/swift,calebd/swift,glessard/swift,hughbe/swift,rudkx/swift,huonw/swift,apple/swift,jopamer/swift,milseman/swift,aschwaighofer/swift,shajrawi/swift,parkera/swift,CodaFi/swift,xwu/swift,swiftix/swift,tjw/swift,amraboelela/swift,felix91gr/swift,amraboelela/swift,jtbandes/swift,deyton/swift,CodaFi/swift,shahmishal/swift,tjw/swift,gribozavr/swift,karwa/swift,danielmartin/swift,zisko/swift,zisko/swift,practicalswift/swift,roambotics/swift,jopamer/swift,huonw/swift,xwu/swift,allevato/swift,Jnosh/swift,shahmishal/swift,hughbe/swift,rudkx/swift,amraboelela/swift,milseman/swift,lorentey/swift,frootloops/swift,austinzheng/swift,CodaFi/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