[String] Speed up UTF-8 initialization from non-stdlib types
[String] Speed up UTF-8 initialization from non-stdlib types

Avoid generic code paths if initializing for UTF-8 (the vast majority
of the time) from a non-stdlib type (such as Data).

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