[stdlib] Fix incorrect Float16 extension
[stdlib] Fix incorrect Float16 extension

This extension (introduced in https://github.com/apple/swift/pull/35264) was placed in a file location where it wasn’t correctly guarded against mentioning Float16 on macOS/x86_64, so the generated .swiftinterface file included a reference to an unavailable declaration. (The dummy stand-in Float16 type that we currently use on Intel macOS.)

Moving the declaration out of the “AnyHashable” section and into a file region that’s more suitable for it (i.e., enclosed in `#if !((os(macOS) || targetEnvironment(macCatalyst)) && arch(x86_64))`) resolves the issue.

rdar://76025365

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