[Runtime] Only cache completed type metadata for associated type witnesses.
[Runtime] Only cache completed type metadata for associated type witnesses.

This is the scheme used for metadata caches elsewhere, and it
eliminates the need to check the metadata state along the hot path of
swift_getAssociatedTypeWitness().

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