[AST] Make sure that hole types are always allocated in `ConstraintSolver` arena
[AST] Make sure that hole types are always allocated in `ConstraintSolver` arena

Since `HoleType` directly as well as other types which could contain holes
are bound to a lifetime of constraint system that created them, we need to
make sure that such types are always allocated using `ConstraintSolver`
arena instead of a permanent one.

apple/swift,jmgc/swift,JGiola/swift,atrick/swift,jmgc/swift,jmgc/swift,nathawes/swift,glessard/swift,xwu/swift,rudkx/swift,gregomni/swift,hooman/swift,CodaFi/swift,glessard/swift,atrick/swift,jmgc/swift,atrick/swift,rudkx/swift,CodaFi/swift,ahoppen/swift,tkremenek/swift,parkera/swift,jmgc/swift,xwu/swift,JGiola/swift,CodaFi/swift,hooman/swift,atrick/swift,xwu/swift,benlangmuir/swift,parkera/swift,CodaFi/swift,parkera/swift,atrick/swift,gregomni/swift,gregomni/swift,roambotics/swift,roambotics/swift,gregomni/swift,ahoppen/swift,nathawes/swift,jmgc/swift,xwu/swift,benlangmuir/swift,glessard/swift,tkremenek/swift,hooman/swift,parkera/swift,xwu/swift,atrick/swift,rudkx/swift,ahoppen/swift,benlangmuir/swift,xwu/swift,apple/swift,rudkx/swift,parkera/swift,apple/swift,apple/swift,JGiola/swift,glessard/swift,parkera/swift,glessard/swift,hooman/swift,benlangmuir/swift,CodaFi/swift,gregomni/swift,gregomni/swift,parkera/swift,roambotics/swift,hooman/swift,rudkx/swift,hooman/swift,CodaFi/swift,tkremenek/swift,xwu/swift,tkremenek/swift,nathawes/swift,apple/swift,tkremenek/swift,rudkx/swift,nathawes/swift,roambotics/swift,JGiola/swift,roambotics/swift,nathawes/swift,ahoppen/swift,jmgc/swift,benlangmuir/swift,JGiola/swift,apple/swift,ahoppen/swift,ahoppen/swift,nathawes/swift,roambotics/swift,tkremenek/swift,parkera/swift,glessard/swift,CodaFi/swift,nathawes/swift,benlangmuir/swift,hooman/swift,tkremenek/swift,JGiola/swift