[SE-0466] Account for nonisolated functions and extensions, too#2916

DougGregor wants to merge 2 commits intoswiftlang:mainswiftlang/swift-evolution:mainfrom

DougGregor:se-0466-local-types-and-extensionsDougGregor/swift-evolution:se-0466-local-types-and-extensionsCopy head branch name to clipboard