[SIL.rst] Add docs for copy_unowned_value and copy_unmanaged_value.
[SIL.rst] Add docs for copy_unowned_value and copy_unmanaged_value.

This commit adds docs for copy_unmanaged_value to SIL.rst as requested by
@eeckstein in #26839. I noticed while doing the PR that copy_unowned_value was
also not documented, so I added docs for it as well as a bonus. = ).

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