[ClangImporter] Add a comment to 'recursivelySubstituteBaseType' (#15381)
[ClangImporter] Add a comment to 'recursivelySubstituteBaseType' (#15381)

As Doug pointed out in the original review where this went in, this
isn't the normal way to do a type substitution. However, all the usual
methods depend on the conformance's generic signature being fully
filled in. Add a comment because, well, I don't have a better answer.
airspeedswift/swift,shajrawi/swift,shahmishal/swift,shahmishal/swift,practicalswift/swift,aschwaighofer/swift,karwa/swift,gribozavr/swift,austinzheng/swift,parkera/swift,gregomni/swift,JGiola/swift,roambotics/swift,xedin/swift,sschiau/swift,natecook1000/swift,aschwaighofer/swift,hooman/swift,benlangmuir/swift,sschiau/swift,huonw/swift,gribozavr/swift,rudkx/swift,tkremenek/swift,tjw/swift,karwa/swift,devincoughlin/swift,CodaFi/swift,parkera/swift,hooman/swift,practicalswift/swift,stephentyrone/swift,apple/swift,aschwaighofer/swift,harlanhaskins/swift,lorentey/swift,xwu/swift,karwa/swift,tkremenek/swift,amraboelela/swift,practicalswift/swift,alblue/swift,karwa/swift,atrick/swift,atrick/swift,shahmishal/swift,amraboelela/swift,allevato/swift,karwa/swift,ahoppen/swift,practicalswift/swift,xedin/swift,ahoppen/swift,xwu/swift,danielmartin/swift,karwa/swift,shajrawi/swift,jopamer/swift,gregomni/swift,lorentey/swift,natecook1000/swift,jckarter/swift,karwa/swift,jopamer/swift,rudkx/swift,danielmartin/swift,austinzheng/swift,huonw/swift,CodaFi/swift,natecook1000/swift,parkera/swift,roambotics/swift,gribozavr/swift,JGiola/swift,jopamer/swift,CodaFi/swift,apple/swift,jopamer/swift,airspeedswift/swift,stephentyrone/swift,rudkx/swift,allevato/swift,austinzheng/swift,shajrawi/swift,glessard/swift,glessard/swift,atrick/swift,gregomni/swift,brentdax/swift,stephentyrone/swift,tkremenek/swift,atrick/swift,brentdax/swift,CodaFi/swift,jopamer/swift,ahoppen/swift,allevato/swift,devincoughlin/swift,austinzheng/swift,nathawes/swift,aschwaighofer/swift,shahmishal/swift,devincoughlin/swift,karwa/swift,jmgc/swift,alblue/swift,parkera/swift,huonw/swift,sschiau/swift,amraboelela/swift,xedin/swift,huonw/swift,devincoughlin/swift,CodaFi/swift,tjw/swift,parkera/swift,airspeedswift/swift,jckarter/swift,devincoughlin/swift,stephentyrone/swift,practicalswift/swift,amraboelela/swift,shajrawi/swift,jmgc/swift,nathawes/swift,stephentyrone/swift,danielmartin/swift,danielmartin/swift,aschwaighofer/swift,danielmartin/swift,tjw/swift,parkera/swift,harlanhaskins/swift,xwu/swift,amraboelela/swift,devincoughlin/swift,brentdax/swift,sschiau/swift,rudkx/swift,austinzheng/swift,lorentey/swift,benlangmuir/swift,sschiau/swift,tkremenek/swift,shajrawi/swift,harlanhaskins/swift,airspeedswift/swift,jmgc/swift,atrick/swift,tjw/swift,lorentey/swift,gribozavr/swift,huonw/swift,tjw/swift,hooman/swift,lorentey/swift,xwu/swift,nathawes/swift,shajrawi/swift,brentdax/swift,atrick/swift,gribozavr/swift,shajrawi/swift,jopamer/swift,alblue/swift,sschiau/swift,xedin/swift,gregomni/swift,natecook1000/swift,natecook1000/swift,jckarter/swift,JGiola/swift,benlangmuir/swift,aschwaighofer/swift,lorentey/swift,parkera/swift,brentdax/swift,sschiau/swift,xwu/swift,jopamer/swift,lorentey/swift,harlanhaskins/swift,ahoppen/swift,xedin/swift,gregomni/swift,gribozavr/swift,hooman/swift,roambotics/swift,stephentyrone/swift,harlanhaskins/swift,gribozavr/swift,benlangmuir/swift,shahmishal/swift,glessard/swift,airspeedswift/swift,nathawes/swift,natecook1000/swift,JGiola/swift,apple/swift,JGiola/swift,aschwaighofer/swift,roambotics/swift,apple/swift,amraboelela/swift,shahmishal/swift,danielmartin/swift,alblue/swift,apple/swift,airspeedswift/swift,glessard/swift,tkremenek/swift,rudkx/swift,tjw/swift,benlangmuir/swift,JGiola/swift,brentdax/swift,ahoppen/swift,alblue/swift,tkremenek/swift,gregomni/swift,tkremenek/swift,CodaFi/swift,benlangmuir/swift,brentdax/swift,nathawes/swift,danielmartin/swift,alblue/swift,glessard/swift,huonw/swift,huonw/swift,sschiau/swift,practicalswift/swift,jckarter/swift,xwu/swift,nathawes/swift,shahmishal/swift,devincoughlin/swift,airspeedswift/swift,parkera/swift,austinzheng/swift,practicalswift/swift,xedin/swift,tjw/swift,hooman/swift,jckarter/swift,gribozavr/swift,allevato/swift,hooman/swift,xwu/swift,apple/swift,alblue/swift,lorentey/swift,nathawes/swift,practicalswift/swift,roambotics/swift,xedin/swift,stephentyrone/swift,jckarter/swift,allevato/swift,allevato/swift,jmgc/swift,harlanhaskins/swift,rudkx/swift,jmgc/swift,jmgc/swift,jckarter/swift,harlanhaskins/swift,amraboelela/swift,shahmishal/swift,jmgc/swift,shajrawi/swift,ahoppen/swift,natecook1000/swift,CodaFi/swift,roambotics/swift,austinzheng/swift,allevato/swift,devincoughlin/swift,xedin/swift,glessard/swift,hooman/swift