[gardening] Add comments explaining what alloc_stack [dynamic_lifetime] means.
[gardening] Add comments explaining what alloc_stack [dynamic_lifetime] means.

Found the meaning by looking at when Definite Initialization marks alloc_stack
with that marker.

For those who are unware like me, it means the liveness of the value in the
alloc_stack is conditional in some way (i.e. conditional init, destroy, etc).

jmgc/swift,benlangmuir/swift,jckarter/swift,xwu/swift,xwu/swift,parkera/swift,nathawes/swift,hooman/swift,jckarter/swift,atrick/swift,glessard/swift,tkremenek/swift,gregomni/swift,nathawes/swift,harlanhaskins/swift,JGiola/swift,apple/swift,harlanhaskins/swift,apple/swift,glessard/swift,roambotics/swift,jckarter/swift,nathawes/swift,tkremenek/swift,atrick/swift,glessard/swift,aschwaighofer/swift,atrick/swift,allevato/swift,ahoppen/swift,apple/swift,roambotics/swift,CodaFi/swift,JGiola/swift,harlanhaskins/swift,glessard/swift,jckarter/swift,stephentyrone/swift,aschwaighofer/swift,airspeedswift/swift,CodaFi/swift,atrick/swift,jmgc/swift,CodaFi/swift,stephentyrone/swift,nathawes/swift,hooman/swift,rudkx/swift,hooman/swift,hooman/swift,gregomni/swift,jckarter/swift,stephentyrone/swift,ahoppen/swift,glessard/swift,ahoppen/swift,ahoppen/swift,apple/swift,hooman/swift,tkremenek/swift,gregomni/swift,jmgc/swift,xwu/swift,benlangmuir/swift,parkera/swift,stephentyrone/swift,CodaFi/swift,roambotics/swift,allevato/swift,allevato/swift,jckarter/swift,parkera/swift,parkera/swift,aschwaighofer/swift,allevato/swift,stephentyrone/swift,rudkx/swift,nathawes/swift,glessard/swift,parkera/swift,harlanhaskins/swift,allevato/swift,ahoppen/swift,CodaFi/swift,atrick/swift,parkera/swift,xwu/swift,roambotics/swift,CodaFi/swift,xwu/swift,apple/swift,jmgc/swift,stephentyrone/swift,aschwaighofer/swift,airspeedswift/swift,airspeedswift/swift,JGiola/swift,jmgc/swift,jmgc/swift,airspeedswift/swift,allevato/swift,roambotics/swift,atrick/swift,xwu/swift,hooman/swift,benlangmuir/swift,CodaFi/swift,harlanhaskins/swift,parkera/swift,rudkx/swift,airspeedswift/swift,JGiola/swift,xwu/swift,gregomni/swift,benlangmuir/swift,roambotics/swift,parkera/swift,jmgc/swift,allevato/swift,rudkx/swift,hooman/swift,airspeedswift/swift,harlanhaskins/swift,stephentyrone/swift,JGiola/swift,aschwaighofer/swift,nathawes/swift,tkremenek/swift,benlangmuir/swift,airspeedswift/swift,rudkx/swift,jckarter/swift,rudkx/swift,tkremenek/swift,gregomni/swift,aschwaighofer/swift,gregomni/swift,nathawes/swift,harlanhaskins/swift,tkremenek/swift,aschwaighofer/swift,benlangmuir/swift,JGiola/swift,tkremenek/swift,apple/swift,ahoppen/swift