SILGen: Fix materializeForSet emission for upcoming witness thunk signature change
SILGen: Fix materializeForSet emission for upcoming witness thunk signature change

Recover the type of 'self' from the requirement's synthetic environment,
instead of assuming it is the conforming type.

This allows us to model witness thunks where 'self' has a
class-constrained generic parameter type instead of the type
of the class itself.

No functional change yet, just a simplification.

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